Mojom: Blanket change to mark all pointer/handle fields as nullable.

mojo/services/gles2/command_buffer.mojom

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module mojo {
 
 struct CommandBufferState {
   int32 num_entries;
   int32 get_offset;
   int32 put_offset;
   int32 token;
   int32 error;  // TODO(piman): enum
   int32 context_lost_reason;  // TODO(piman): enum
   uint32 generation;
 };
 
 interface CommandBufferSyncClient {
   DidInitialize(bool success);
-  DidMakeProgress(CommandBufferState state);
+  DidMakeProgress(CommandBufferState? state);
 };
 
 [Client=CommandBufferClient]
 interface CommandBuffer {
-  Initialize(CommandBufferSyncClient sync_client,
-             handle<shared_buffer> shared_state);
+  Initialize(CommandBufferSyncClient? sync_client,
+             handle<shared_buffer>? shared_state);
   SetGetBuffer(int32 buffer);
   Flush(int32 put_offset);
   MakeProgress(int32 last_get_offset);
   RegisterTransferBuffer(
-      int32 id, handle<shared_buffer> transfer_buffer, uint32 size);
+      int32 id, handle<shared_buffer>? transfer_buffer, uint32 size);
   DestroyTransferBuffer(int32 id);
   Echo() => ();
 
   // TODO(piman): sync points
 };
 
 interface CommandBufferClient {
   DidDestroy();
   LostContext(int32 lost_reason);  // TODO(piman): enum
 };
 
 }