Don't create a gin::IsolateHolder in extensions unittests.

extensions/renderer/script_context_set_unittest.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 "base/message_loop/message_loop.h"
 #include "extensions/common/extension.h"
 #include "extensions/common/features/feature.h"
 #include "extensions/renderer/script_context.h"
 #include "extensions/renderer/script_context_set.h"
 #include "gin/public/context_holder.h"
-#include "gin/public/isolate_holder.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/WebKit/public/web/WebFrame.h"
 #include "v8/include/v8.h"
 
 namespace extensions {
 
 TEST(ScriptContextSet, Lifecycle) {
   base::MessageLoop loop;
 
   ScriptContextSet context_set;
 
   v8::Isolate* isolate = v8::Isolate::GetCurrent();
-  gin::IsolateHolder isolate_holder(isolate, NULL);
   v8::HandleScope handle_scope(isolate);
   gin::ContextHolder context_holder(isolate);
   context_holder.SetContext(v8::Context::New(isolate));
 
   // Dirty hack, but we don't actually need the frame, and this is easier than
   // creating a whole webview.
   blink::WebFrame* frame = reinterpret_cast<blink::WebFrame*>(1);
   const Extension* extension = NULL;
   ScriptContext* context =
       new ScriptContext(context_holder.context(),
@@ skipping 19 matching lines @@
   EXPECT_EQ(1u, set_copy.size());
 
   // After removal, the context should be marked for destruction.
   EXPECT_FALSE(context->web_frame());
 
   // Run loop to do the actual deletion.
   loop.RunUntilIdle();
 }
 
 }  // namespace extensions