[Extensions] Don't pass empty value to V8Converter in OnJSInjectionCompleted

extensions/renderer/script_injection.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/script_injection.h"
 
 #include <map>
 
 #include "base/lazy_instance.h"
 #include "base/metrics/histogram.h"
@@ skipping 287 matching lines @@
 
 void ScriptInjection::OnJsInjectionCompleted(
     blink::WebLocalFrame* frame,
     const blink::WebVector<v8::Local<v8::Value> >& results) {
   DCHECK(running_frames_ > 0);
   --running_frames_;
 
   bool expects_results = injector_->ExpectsResults();
   if (expects_results) {
     scoped_ptr<base::Value> result;
-    if (!results.isEmpty()) {
+    if (!results.isEmpty() && !results[0].IsEmpty()) {
       // Right now, we only support returning single results (per frame).
       scoped_ptr<content::V8ValueConverter> v8_converter(
           content::V8ValueConverter::create());
       // 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 = frame->mainWorldScriptContext();
       result.reset(v8_converter->FromV8Value(results[0], context));
     }
@@ skipping 24 matching lines @@
   std::vector<std::string> css_sources =
       injector_->GetCssSources(run_location_);
   for (std::vector<std::string>::const_iterator iter = css_sources.begin();
        iter != css_sources.end();
        ++iter) {
     frame->document().insertStyleSheet(blink::WebString::fromUTF8(*iter));
   }
 }
 
 }  // namespace extensions