Mojo: Add the ability to notify a Mojo Channel that it's going to be destroyed soon.

mojo/embedder/embedder.cc

 // 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.
 
 #include "mojo/embedder/embedder.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 155 matching lines @@
 
   channel_info->channel->Shutdown();
   delete channel_info;
 }
 
 // TODO(vtl): Write tests for this.
 void DestroyChannel(ChannelInfo* channel_info) {
   DCHECK(channel_info);
   DCHECK(channel_info->io_thread_task_runner);
 
+  if (!channel_info->channel) {
+    // Presumably, |Init()| on the channel failed.
+    return;
+  }
+
+  channel_info->channel->WillShutdownSoon();
   channel_info->io_thread_task_runner->PostTask(
       FROM_HERE, base::Bind(&DestroyChannelOnIOThread, channel_info));
 }
 
+void WillDestroyChannelSoon(ChannelInfo* channel_info) {
+  DCHECK(channel_info);
+  channel_info->channel->WillShutdownSoon();
+}
+
 MojoResult CreatePlatformHandleWrapper(
     ScopedPlatformHandle platform_handle,
     MojoHandle* platform_handle_wrapper_handle) {
   DCHECK(platform_handle_wrapper_handle);
 
   scoped_refptr<system::Dispatcher> dispatcher(
       new system::PlatformHandleDispatcher(platform_handle.Pass()));
 
   system::Core* core = system::entrypoints::GetCore();
   DCHECK(core);
@@ skipping 24 matching lines @@
 
   *platform_handle =
       static_cast<system::PlatformHandleDispatcher*>(dispatcher.get())
           ->PassPlatformHandle()
           .Pass();
   return MOJO_RESULT_OK;
 }
 
 }  // namespace embedder
 }  // namespace mojo