Added proto files for upcoming debug messages (subject to change).

To compile, run:
$ protoc --proto_path=. --python_out=. *.proto

agent.proto

@@ -0,0 +1,86 @@
+// Licensed to the Apache Software Foundation (ASF) under one                 
+// or more contributor license agreements.  See the NOTICE file               
+// distributed with this work for additional information                      
+// regarding copyright ownership.  The ASF licenses this file                 
+// to you under the Apache License, Version 2.0 (the                          
+// "License"); you may not use this file except in compliance                 
+// with the License.  You may obtain a copy of the License at                 
+//
+//     http://www.apache.org/licenses/LICENSE-2.0                             
+//  
+// Unless required by applicable law or agreed to in writing, software        
+// distributed under the License is distributed on an "AS IS" BASIS,          
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.   
+// See the License for the specific language governing permissions and        
+// limitations under the License.                                             
+
+import "mesos.proto";
+
+package mesos.agent;
+
+option java_package = "org.apache.mesos.agent";
+option java_outer_classname = "Protos";
+
+
+message Call {
+  enum Type {
+    UNKNOWN = 0;
+
+    // Launches a nested container whose life-cycle is tied to the 
+    // lifetime of the connection used to make this call. Once the 
+    // agent receives the request, it will hold onto it until the 
+    // container runs to completion or there is an error. Upon 
+    // success, a 200 response will be initiated with an “infinite” 
+    // chunked response (but no data will ever be sent over this 
+    // connection). On error, an appropriate 400 error will be    
+    // returned. If the connection is ever broken by the client, the 
+    // container will be destroyed.       
+    LAUNCH_NESTED_CONTAINER_SESSION = 17;
+
+    // Attaches a remote client to the the input/output of the 
+    // entrypoint of a container. All input/output data is packed into 
+    // I/O messages and interleaved with control messages sent between 
+    // a client and the agent. A single chunked request is used to 
+    // stream messages to the agent over the input stream, and a 
+    // single chunked response is used to stream messages to the  
+    // client over the output stream.
+    ATTACH_CONTAINER_OUTPUT = 18;
+    ATTACH_CONTAINER_INPUT = 19;
+  }
+
+
+  message LaunchNestedContainerSession {
+    required ContainerID container_id = 1;
+    optional CommandInfo command = 2;
+
+    // NOTE: The following should be backported
+    // into the TaskInfo message post-mvp
+    optional TtyInfo tty_info = 3;
+    optional bool interactive = 4;
+
+    // NOTE: The following field will be added post-mvp to
+    // support mounting a new image in the nested container.
+    // optional ContainerInfo container = 5;
+  }
+
+  message AttachContainerOutput {
+    required ContainerID container_id = 1;
+  }
+
+  message AttachContainerInput {
+    enum Type {
+      UNKNOWN = 0;
+
+      CONTAINER_ID = 1;
+      PROCESS_IO = 2;
+    }
+
+    optional Type type = 1;
+    optional ContainerID container_id = 2;
+    optional ProcessIO process_io = 3;
+  }
+
+  optional LaunchNestedContainerSession launch_nested_container_session = 9;
+  optional AttachContainerOutput attach_container_output = 10;
+  optional AttachContainerInput attach_container_input = 11;
+}

mesos.proto

@@ -0,0 +1,164 @@
+// Licensed to the Apache Software Foundation (ASF) under one                 
+// or more contributor license agreements.  See the NOTICE file               
+// distributed with this work for additional information                      
+// regarding copyright ownership.  The ASF licenses this file                 
+// to you under the Apache License, Version 2.0 (the                          
+// "License"); you may not use this file except in compliance                 
+// with the License.  You may obtain a copy of the License at                 
+//
+//     http://www.apache.org/licenses/LICENSE-2.0                             
+//  
+// Unless required by applicable law or agreed to in writing, software        
+// distributed under the License is distributed on an "AS IS" BASIS,          
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.   
+// See the License for the specific language governing permissions and        
+// limitations under the License.                                             
+
+package mesos;
+
+option java_package = "org.apache.mesos";                                     
+option java_outer_classname = "Protos";                                       
+
+
+message TtyInfo {
+  message WindowSize {
+    required uint32 rows = 1;
+    required uint32 columns = 2;
+  }
+
+  optional WindowSize window_size = 1;
+}
+
+
+message ProcessIO {
+  enum Type {
+    UNKNOWN = 0;
+
+    DATA = 1;
+    CONTROL = 2;
+  }
+
+  message Data {
+    enum Type {
+      UNKNOWN = 0;
+
+      STDIN = 1;
+      STDOUT = 2;
+      STDERR = 3;
+    }
+
+    optional Type type = 1;
+    optional bytes data = 2;
+  }
+
+  message Control {
+    enum Type {
+      UNKNOWN = 0;
+
+      TTY_INFO = 1;
+    }
+
+    optional Type type = 1;
+    optional TtyInfo tty_info = 2;
+  }
+
+  optional Type type = 1;
+  optional Data data = 2;
+  optional Control control = 3;
+}
+
+
+/**
+ * ID used to uniquely identify a container. If the `parent` is not
+ * specified, the ID is a UUID generated by the agent to uniquely
+ * identify the container of an executor run. If the `parent` field is
+ * specified, it represents a nested container.
+ */
+message ContainerID {
+  required string value = 1;
+  optional ContainerID parent = 2;
+}
+
+
+/**
+ * Describes a command, executed via: '/bin/sh -c value'. Any URIs specified
+ * are fetched before executing the command.  If the executable field for an
+ * uri is set, executable file permission is set on the downloaded file.
+ * Otherwise, if the downloaded file has a recognized archive extension
+ * (currently [compressed] tar and zip) it is extracted into the executor's
+ * working directory. This extraction can be disabled by setting `extract` to
+ * false. In addition, any environment variables are set before executing
+ * the command (so they can be used to "parameterize" your command).
+ */
+message CommandInfo {
+  message URI {
+    required string value = 1;
+    optional bool executable = 2;
+
+    // In case the fetched file is recognized as an archive, extract
+    // its contents into the sandbox. Note that a cached archive is
+    // not copied from the cache to the sandbox in case extraction
+    // originates from an archive in the cache.
+    optional bool extract = 3 [default = true];
+
+    // If this field is "true", the fetcher cache will be used. If not,
+    // fetching bypasses the cache and downloads directly into the
+    // sandbox directory, no matter whether a suitable cache file is
+    // available or not. The former directs the fetcher to download to
+    // the file cache, then copy from there to the sandbox. Subsequent
+    // fetch attempts with the same URI will omit downloading and copy
+    // from the cache as long as the file is resident there. Cache files
+    // may get evicted at any time, which then leads to renewed
+    // downloading. See also "docs/fetcher.md" and
+    // "docs/fetcher-cache-internals.md".
+    optional bool cache = 4;
+
+    // The fetcher's default behavior is to use the URI string's basename to
+    // name the local copy. If this field is provided, the local copy will be
+    // named with its value instead. If there is a directory component (which
+    // must be a relative path), the local copy will be stored in that
+    // subdirectory inside the sandbox.
+    optional string output_file = 5;
+  }
+
+  repeated URI uris = 1;
+
+  optional Environment environment = 2;
+
+  // There are two ways to specify the command:
+  // 1) If 'shell == true', the command will be launched via shell
+  //		(i.e., /bin/sh -c 'value'). The 'value' specified will be
+  //		treated as the shell command. The 'arguments' will be ignored.
+  // 2) If 'shell == false', the command will be launched by passing
+  //		arguments to an executable. The 'value' specified will be
+  //		treated as the filename of the executable. The 'arguments'
+  //		will be treated as the arguments to the executable. This is
+  //		similar to how POSIX exec families launch processes (i.e.,
+  //		execlp(value, arguments(0), arguments(1), ...)).
+  // NOTE: The field 'value' is changed from 'required' to 'optional'
+  // in 0.20.0. It will only cause issues if a new framework is
+  // connecting to an old master.
+  optional bool shell = 6 [default = true];
+  optional string value = 3;
+  repeated string arguments = 7;
+
+  // Enables executor and tasks to run as a specific user. If the user
+  // field is present both in FrameworkInfo and here, the CommandInfo
+  // user value takes precedence.
+  optional string user = 5;
+}
+
+
+/**
+* Describes a collection of environment variables. This is used with
+* CommandInfo in order to set environment variables before running a
+* command.
+*/
+message Environment {
+  message Variable {
+    required string name = 1;
+    required string value = 2;
+  }
+
+  repeated Variable variables = 1;
+}