Introduce a Gin class instead of using global functions to control gin

gin/test/v8_test.cc

 // Copyright 2013 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 "gin/test/v8_test.h"
 
+#include "gin/gin.h"
+
 using v8::Context;
 using v8::Local;
 using v8::HandleScope;
-using v8::Isolate;
 
 namespace gin {
 
 V8Test::V8Test() {
 }
 
 V8Test::~V8Test() {
 }
 
 void V8Test::SetUp() {
-  isolate_ = Isolate::GetCurrent();
-  HandleScope handle_scope(isolate_);
-  context_.Reset(isolate_, Context::New(isolate_));
-  Local<Context>::New(isolate_, context_)->Enter();
+  instance_.reset(new gin::Gin);
+  instance_->isolate()->Enter();
+  HandleScope handle_scope(instance_->isolate());
+  context_.Reset(instance_->isolate(), Context::New(instance_->isolate()));
+  Local<Context>::New(instance_->isolate(), context_)->Enter();
 }
 
 void V8Test::TearDown() {
-  HandleScope handle_scope(isolate_);
-  Local<Context>::New(isolate_, context_)->Exit();
-  context_.Reset();
+  {
+    HandleScope handle_scope(instance_->isolate());
+    Local<Context>::New(instance_->isolate(), context_)->Exit();
+    context_.Reset();
+  }
+  instance_->isolate()->Exit();
+  instance_.reset();
 }
 
 }  // namespace gin