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

ppapi/cpp/private/tcp_socket_private.h

Index: ppapi/cpp/private/tcp_socket_private.h
diff --git a/ppapi/cpp/private/tcp_socket_private.h b/ppapi/cpp/private/tcp_socket_private.h
index b8728b46793e51db7e9fdf68e278a0388ad93373..415a1eded4ba4faea940480e89d57b8bce9250de 100644
--- a/ppapi/cpp/private/tcp_socket_private.h
+++ b/ppapi/cpp/private/tcp_socket_private.h
@@ -12,11 +12,11 @@
 namespace pp {
 
 class CompletionCallback;
-class Instance;
+class InstanceHandle;
 
 class TCPSocketPrivate : public Resource {
  public:
-  explicit TCPSocketPrivate(Instance* instance);
+  explicit TCPSocketPrivate(const InstanceHandle& instance);
 
   // Returns true if the required interface is available.
   static bool IsAvailable();