Don't serialize extension user script injection results unless the extension

chrome/renderer/extensions/user_script_scheduler.cc

Index: chrome/renderer/extensions/user_script_scheduler.cc
diff --git a/chrome/renderer/extensions/user_script_scheduler.cc b/chrome/renderer/extensions/user_script_scheduler.cc
index f3ef86f615be1fcbe9eda9f136be08e96f69ad55..558ada07830d5ac657c167d03355910a6b558e6a 100644
--- a/chrome/renderer/extensions/user_script_scheduler.cc
+++ b/chrome/renderer/extensions/user_script_scheduler.cc
@@ -11,6 +11,7 @@
 #include "chrome/common/extensions/extension_messages.h"
 #include "chrome/common/extensions/permissions/permissions_data.h"
 #include "chrome/renderer/chrome_render_process_observer.h"
+#include "chrome/renderer/extensions/chrome_v8_context.h"
 #include "chrome/renderer/extensions/dispatcher.h"
 #include "chrome/renderer/extensions/dom_activity_logger.h"
 #include "chrome/renderer/extensions/extension_groups.h"
@@ -199,12 +200,11 @@ void UserScriptScheduler::ExecuteCodeImpl(
       }
 
       WebScriptSource source(WebString::fromUTF8(params.code));
-      v8::Isolate* isolate = v8::Isolate::GetCurrent();
-      v8::HandleScope scope(isolate);
+      v8::HandleScope scope;
 
       scoped_ptr<content::V8ValueConverter> v8_converter(
           content::V8ValueConverter::create());
-      v8::Handle<v8::Value> script_value;
+      v8::Local<v8::Value> script_value;
 
       if (params.in_main_world) {
         DOMActivityLogger::AttachToWorld(
@@ -232,15 +232,17 @@ void UserScriptScheduler::ExecuteCodeImpl(
         if (results.size() == 1 && !results[0].IsEmpty())
           script_value = results[0];
       }
-      if (!script_value.IsEmpty()) {
-        v8::Local<v8::Context> context = v8::Context::New(isolate);
-        base::Value* base_val =
-            v8_converter->FromV8Value(script_value, context);
+
+      if (params.wants_result && !script_value.IsEmpty()) {
+        // It's safe to always use the main world context when converting here.
+        // V8ValueConverterImpl shouldn't actually care about the context scope,
+        // and it switches to v8::Object's creation context when encountered.
+        v8::Local<v8::Context> context = child_frame->mainWorldScriptContext();
+        base::Value* result = v8_converter->FromV8Value(script_value, context);
         // Always append an execution result (i.e. no result == null result) so
         // that |execution_results| lines up with the frames.
-        execution_results.Append(base_val ? base_val :
-                                            base::Value::CreateNullValue());
-        script_value.Clear();
+        execution_results.Append(
+            result ? result : base::Value::CreateNullValue());
       }
     } else {
       child_frame->document().insertUserStyleSheet(