These sources are already compiled into the V8 artifacts, and are not
compiled as part of the runtime.

This line shadows a v8::Context already present in the outer scope, so
it's not necessary.

…cient

Two changes suggested by Android Studio. We avoid copying the string
argument, and we check quicker whether the map is empty without having to
count all the entries.

JSWrapperConstructorCallback isn't used anywhere.

Noticed while fixing static initialization of keywords set, see next
commit.