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

extensions/renderer/module_system.cc

Index: extensions/renderer/module_system.cc
diff --git a/extensions/renderer/module_system.cc b/extensions/renderer/module_system.cc
index ab265fade68c92cba7f902d96365371fe22f1c42..1f337643476d06ad230eab1fb4949e61ec616a8f 100644
--- a/extensions/renderer/module_system.cc
+++ b/extensions/renderer/module_system.cc
@@ -230,9 +230,10 @@ v8::Local<v8::Value> ModuleSystem::RequireForJsInner(
 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(