gin: Make it possible to use gin array buffers when running on top of blink

gin/array_buffer.cc

Index: gin/array_buffer.cc
diff --git a/gin/array_buffer.cc b/gin/array_buffer.cc
index ee9f2a5867b21a970daec17881ba4411a2631762..42948a7882580ff87982b708659dead5e83d1420 100644
--- a/gin/array_buffer.cc
+++ b/gin/array_buffer.cc
@@ -2,10 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "gin/array_buffer.h"
-
 #include <stdlib.h>
 
+#include "gin/array_buffer.h"
+#include "gin/per_isolate_data.h"
+
 namespace gin {
 
 COMPILE_ASSERT(V8_ARRAY_BUFFER_INTERNAL_FIELD_COUNT == 2,
@@ -72,6 +73,7 @@ class ArrayBuffer::Private : public base::RefCounted<ArrayBuffer::Private> {
 
   v8::Persistent<v8::ArrayBuffer> array_buffer_;
   scoped_refptr<Private> self_reference_;
+  v8::Isolate* isolate_;
   void* buffer_;
   size_t length_;
 };
@@ -87,8 +89,9 @@ scoped_refptr<ArrayBuffer::Private> ArrayBuffer::Private::From(
 
 ArrayBuffer::Private::Private(v8::Isolate* isolate,
                               v8::Handle<v8::ArrayBuffer> array)
-    : array_buffer_(isolate, array) {
+    : array_buffer_(isolate, array), isolate_(isolate) {
   // Take ownership of the array buffer.
+  CHECK(!array->IsExternal());
   v8::ArrayBuffer::Contents contents = array->Externalize();
   buffer_ = contents.Data();
   length_ = contents.ByteLength();
@@ -100,7 +103,7 @@ ArrayBuffer::Private::Private(v8::Isolate* isolate,
 }
 
 ArrayBuffer::Private::~Private() {
-  ArrayBufferAllocator::SharedInstance()->Free(buffer_, length_);
+  PerIsolateData::From(isolate_)->allocator()->Free(buffer_, length_);
 }
 
 void ArrayBuffer::Private::WeakCallback(