Add support for writing unit tests for Mojo-backed apps/extensions APIs.

extensions/renderer/module_system.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "extensions/renderer/module_system.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/stl_util.h"
@@ skipping 212 matching lines @@
     return handle_scope.Escape(exports);
 
   exports = LoadModule(*v8::String::Utf8Value(module_name));
   modules->Set(module_name, exports);
   return handle_scope.Escape(exports);
 }
 
 v8::Local<v8::Value> ModuleSystem::CallModuleMethod(
     const std::string& module_name,
     const std::string& method_name) {
-  v8::HandleScope handle_scope(GetIsolate());
+  v8::EscapableHandleScope handle_scope(GetIsolate());
   v8::Handle<v8::Value> no_args;
-  return CallModuleMethod(module_name, method_name, 0, &no_args);
+  return handle_scope.Escape(
+      CallModuleMethod(module_name, method_name, 0, &no_args));
 }
 
 v8::Local<v8::Value> ModuleSystem::CallModuleMethod(
     const std::string& module_name,
     const std::string& method_name,
     std::vector<v8::Handle<v8::Value> >* args) {
   return CallModuleMethod(
       module_name, method_name, args->size(), vector_as_array(args));
 }
 
@@ skipping 413 matching lines @@
     v8::Handle<v8::Value> value) {
   if (!is_valid())
     return;
   v8::HandleScope handle_scope(GetIsolate());
   v8::Handle<v8::Promise::Resolver> resolver_local(
       v8::Local<v8::Promise::Resolver>::New(GetIsolate(), *resolver));
   resolver_local->Resolve(value);
 }
 
 }  // namespace extensions