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

ppapi/cpp/private/udp_socket_private.h

Index: ppapi/cpp/private/udp_socket_private.h
diff --git a/ppapi/cpp/private/udp_socket_private.h b/ppapi/cpp/private/udp_socket_private.h
index abe434b61631286dda43eca49ba5ec73b402363a..e80091ceea53c068a5a8fd00e43d2a5930c98ddb 100644
--- a/ppapi/cpp/private/udp_socket_private.h
+++ b/ppapi/cpp/private/udp_socket_private.h
@@ -12,11 +12,11 @@
 namespace pp {
 
 class CompletionCallback;
-class Instance;
+class InstanceHandle;
 
 class UDPSocketPrivate : public Resource {
  public:
-  explicit UDPSocketPrivate(Instance* instance);
+  explicit UDPSocketPrivate(const InstanceHandle& instance);
 
   int32_t Bind(const PP_NetAddress_Private* addr,
                const CompletionCallback& callback);