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 85bfb5336a2398f0f8077572aa9cc4a9130c352b..e4cb6e01380df3929531356619913d0c02de549c 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);