Fix crash with pepper 3D on multiple windows in same renderer

chrome/renderer/pepper_platform_context_3d_impl.h

Index: chrome/renderer/pepper_platform_context_3d_impl.h
diff --git a/chrome/renderer/pepper_platform_context_3d_impl.h b/chrome/renderer/pepper_platform_context_3d_impl.h
index dedbc798ef3c46dced6813c7c92dfd560139fee1..cb036835fff0ad50fdc69b440db591aa0d0d2dba 100644
--- a/chrome/renderer/pepper_platform_context_3d_impl.h
+++ b/chrome/renderer/pepper_platform_context_3d_impl.h
@@ -7,6 +7,7 @@
 #include "base/callback.h"
 #include "base/scoped_callback_factory.h"
 #include "base/scoped_ptr.h"
+#include "base/weak_ptr.h"
 #include "webkit/plugins/ppapi/plugin_delegate.h"
 
 #ifdef ENABLE_GPU
@@ -42,7 +43,7 @@ class PlatformContext3DImpl
   bool InitRaw();
   void OnContextLost();
 
-  ggl::Context* parent_context_;
+  base::WeakPtr<ggl::Context> parent_context_;
   scoped_refptr<GpuChannelHost> channel_;
   unsigned int parent_texture_id_;
   CommandBufferProxy* command_buffer_;