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

ppapi/cpp/private/flash_message_loop.h

Index: ppapi/cpp/private/flash_message_loop.h
diff --git a/ppapi/cpp/private/flash_message_loop.h b/ppapi/cpp/private/flash_message_loop.h
index de2af45ce1db1d97a512f794292267890e81c01b..fecb2d6b42d8b2d53d2a8ce61027987783708f40 100644
--- a/ppapi/cpp/private/flash_message_loop.h
+++ b/ppapi/cpp/private/flash_message_loop.h
@@ -10,13 +10,13 @@
 
 namespace pp {
 
-class Instance;
+class InstanceHandle;
 
 namespace flash {
 
 class MessageLoop : public Resource {
  public:
-  explicit MessageLoop(Instance* instance);
+  explicit MessageLoop(const InstanceHandle& instance);
   virtual ~MessageLoop();
 
   static bool IsAvailable();