Add a benchmark exercising property lookups in the immediate prototype.

Summary:
This diff adds a microbenchmark stressing property lookups satisfied
in an object's immediate prototype.  This provides a baseline for a
subsequent diff that optimizes such accesses.

Reviewed By: avp

Differential Revision: D65350534

fbshipit-source-id: 12b1dfdfbc7219d0427b64ca944c7f94d0079368

benchmarks/bench-runner/categories.py

@@ -388,6 +388,10 @@ def __repr__(self):
             "numberArrayReadWrite", "micros/numberArrayReadWrite.js",
             gcMinHeap="1M", gcMaxHeap="1M"
         ),
+        ResourceBenchmark(
+            "protoCache", "micros/protoCache.js",
+            gcMinHeap="1M", gcMaxHeap="1M"
+        ),
     ],
     runByDefault=False,
 )

benchmarks/bench-runner/resource/test-suites/micros/protoCache.js

@@ -0,0 +1,29 @@
+var start = new Date();
+var val = (function () {
+  var proto = {x: 7};
+  var o = Object.create(proto);
+
+  function access(o) {
+    'noinline'
+    // 50 accesses, all found in the proto.
+    return o.x + o.x + o.x + o.x + o.x
+      + o.x  + o.x + o.x + o.x + o.x
+      + o.x  + o.x + o.x + o.x + o.x
+      + o.x  + o.x + o.x + o.x + o.x
+      + o.x  + o.x + o.x + o.x + o.x
+      + o.x  + o.x + o.x + o.x + o.x
+      + o.x  + o.x + o.x + o.x + o.x
+      + o.x  + o.x + o.x + o.x + o.x
+      + o.x  + o.x + o.x + o.x + o.x
+      + o.x  + o.x + o.x + o.x + o.x;
+  }
+  var numIter = 10000000;
+  var sum = 0;
+  for (var i = 0; i < numIter; i++) {
+    sum += access(o);
+  }
+  return sum;
+}());
+var end = new Date();
+print("val: " + val);
+print("Time: " + (end - start));