7 files changed, 34 insertions, 5 deletions
diff --git a/gin/gin.gyp b/gin/gin.gyp
index 8758932..e0ec34c 100644
--- a/gin/gin.gyp
+++ b/gin/gin.gyp
@@ -48,6 +48,7 @@
         'try_catch.cc',
         'try_catch.h',
         'wrapper_info.cc',
+        'public/gin_embedders.h',
         'public/wrapper_info.h',
       ],
     },
diff --git a/gin/modules/console.cc b/gin/modules/console.cc
index b3614a8..de86451 100644
--- a/gin/modules/console.cc
+++ b/gin/modules/console.cc
@@ -28,7 +28,7 @@ void Log(const v8::FunctionCallbackInfo<v8::Value>& info) {
   std::cout << JoinString(messages, ' ') << std::endl;
 }
 
-WrapperInfo g_wrapper_info = {};
+WrapperInfo g_wrapper_info = { kEmbedderNativeGin };
 
 }  // namespace
 
diff --git a/gin/modules/module_registry.cc b/gin/modules/module_registry.cc
index fe9218c..8baa482 100644
--- a/gin/modules/module_registry.cc
+++ b/gin/modules/module_registry.cc
@@ -74,7 +74,7 @@ void Define(const v8::FunctionCallbackInfo<Value>& info) {
   registry->AddPendingModule(args.isolate(), pending.Pass());
 }
 
-WrapperInfo g_wrapper_info = {};
+WrapperInfo g_wrapper_info = { kEmbedderNativeGin };
 
 Local<FunctionTemplate> GetDefineTemplate(Isolate* isolate) {
   PerIsolateData* data = PerIsolateData::From(isolate);
diff --git a/gin/public/gin_embedders.h b/gin/public/gin_embedders.h
new file mode 100644
index 0000000..bffe6e0
--- /dev/null
+++ b/gin/public/gin_embedders.h
@@ -0,0 +1,21 @@
+// 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.
+
+#ifndef GIN_PUBLIC_GIN_EMBEDDERS_H_
+#define GIN_PUBLIC_GIN_EMBEDDERS_H_
+
+namespace gin {
+
+// The GinEmbedder is used to identify the owner of embedder data stored on
+// v8 objects, and is used as in index into the embedder data slots of a
+// v8::Isolate.
+
+enum GinEmbedder {
+  kEmbedderNativeGin,
+  kEmbedderBlink,
+};
+
+}  // namespace gin
+
+#endif  // GIN_PUBLIC_GIN_EMBEDDERS_H_
diff --git a/gin/public/wrapper_info.h b/gin/public/wrapper_info.h
index f1c554e..fe047c0 100644
--- a/gin/public/wrapper_info.h
+++ b/gin/public/wrapper_info.h
@@ -5,10 +5,16 @@
 #ifndef GIN_PUBLIC_WRAPPER_INFO_H_
 #define GIN_PUBLIC_WRAPPER_INFO_H_
 
+#include "gin/public/gin_embedders.h"
 #include "v8/include/v8.h"
 
 namespace gin {
 
+// Gin embedder that use their own WrapperInfo-like structs must ensure that
+// the first field is of type GinEmbedderId and has the correct id set. They
+// also should use kWrapperInfoIndex to start their WrapperInfo-like struct
+// and ensure that all objects have kNumberOfInternalFields internal fields.
+
 enum InternalFields {
   kWrapperInfoIndex,
   kEncodedValueIndex,
@@ -17,7 +23,7 @@ enum InternalFields {
 
 struct WrapperInfo {
   static WrapperInfo* From(v8::Handle<v8::Object> object);
-  // Currently we just use the address of this struct for identity.
+  const GinEmbedder embedder;
 };
 
 }  // namespace gin
diff --git a/gin/test/gtest.cc b/gin/test/gtest.cc
index 2697282..962bd9a 100644
--- a/gin/test/gtest.cc
+++ b/gin/test/gtest.cc
@@ -54,7 +54,7 @@ void ExpectEqual(const v8::FunctionCallbackInfo<v8::Value>& info) {
   EXPECT_TRUE(info[0]->StrictEquals(info[1])) << description;
 }
 
-WrapperInfo g_wrapper_info = {};
+WrapperInfo g_wrapper_info = { kEmbedderNativeGin };
 
 }  // namespace
 
diff --git a/gin/wrapper_info.cc b/gin/wrapper_info.cc
index c1c6774..6bf8316 100644
--- a/gin/wrapper_info.cc
+++ b/gin/wrapper_info.cc
@@ -9,8 +9,9 @@ namespace gin {
 WrapperInfo* WrapperInfo::From(v8::Handle<v8::Object> object) {
   if (object->InternalFieldCount() != kNumberOfInternalFields)
     return NULL;
-  return static_cast<WrapperInfo*>(
+  WrapperInfo* info = static_cast<WrapperInfo*>(
       object->GetAlignedPointerFromInternalField(kWrapperInfoIndex));
+  return info->embedder == kEmbedderNativeGin ? info : NULL;
 }
 
 }  // namespace gin