Convert resources to take an instance key instead of an Instance*.

ppapi/cpp/graphics_3d_client.h

Index: ppapi/cpp/graphics_3d_client.h
diff --git a/ppapi/cpp/graphics_3d_client.h b/ppapi/cpp/graphics_3d_client.h
index 60299cabace8bf6a697f485d3fe4ee6158545d32..5886b8466ba62fee816d21cd53fc759258dab77c 100644
--- a/ppapi/cpp/graphics_3d_client.h
+++ b/ppapi/cpp/graphics_3d_client.h
@@ -6,14 +6,13 @@
 #define PPAPI_CPP_GRAPHICS_3D_CLIENT_H_
 
 #include "ppapi/c/pp_stdint.h"
+#include "ppapi/cpp/instance_handle.h"
 
 /// @file
 /// This file defines the API for callbacks related to 3D.
 
 namespace pp {
 
-class Instance;
-
 // This class provides a C++ interface for callbacks related to 3D. You
 // would normally use multiple inheritance to derive from this class in your
 // instance.
@@ -24,7 +23,7 @@ class Graphics3DClient {
   ///
   /// @param[in] instance The instance that will own the new
   /// <code>Graphics3DClient</code>.
-  explicit Graphics3DClient(Instance* instance);
+  explicit Graphics3DClient(const InstanceHandle& instance);
 
   /// Destructor.
   virtual ~Graphics3DClient();
@@ -34,7 +33,7 @@ class Graphics3DClient {
   virtual void Graphics3DContextLost() = 0;
 
  private:
-  Instance* associated_instance_;
+  InstanceHandle associated_instance_;
 };
 
 }  // namespace pp