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

mojo/embedder/embedder.h

 // 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.
 
 #ifndef MOJO_EMBEDDER_EMBEDDER_H_
 #define MOJO_EMBEDDER_EMBEDDER_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/task_runner.h"
@@ skipping 78 matching lines @@
 // provided to the callback to |CreateChannel()|.
 MOJO_SYSTEM_IMPL_EXPORT void DestroyChannelOnIOThread(
     ChannelInfo* channel_info);
 
 // Destroys a channel (asynchronously) that was created using |CreateChannel()|
 // (note: NOT |CreateChannelOnIOThread()|); may be called from any thread.
 // |channel_info| should be the value provided to the callback to
 // |CreateChannel()|.
 MOJO_SYSTEM_IMPL_EXPORT void DestroyChannel(ChannelInfo* channel_info);
 
+// Inform the channel that it will soon be destroyed (doing so is optional).
+// This may be called from any thread, but the caller must ensure that this is
+// called before |DestroyChannel()| or |DestroyChannelOnIOThread()|.
+MOJO_SYSTEM_IMPL_EXPORT void WillDestroyChannelSoon(ChannelInfo* channel_info);
+
 // Creates a |MojoHandle| that wraps the given |PlatformHandle| (taking
 // ownership of it). This |MojoHandle| can then, e.g., be passed through message
 // pipes. Note: This takes ownership (and thus closes) |platform_handle| even on
 // failure, which is different from what you'd expect from a Mojo API, but it
 // makes for a more convenient embedder API.
 MOJO_SYSTEM_IMPL_EXPORT MojoResult
     CreatePlatformHandleWrapper(ScopedPlatformHandle platform_handle,
                                 MojoHandle* platform_handle_wrapper_handle);
 // Retrieves the |PlatformHandle| that was wrapped into a |MojoHandle| (using
 // |CreatePlatformHandleWrapper()| above). Note that the |MojoHandle| must still
 // be closed separately.
 MOJO_SYSTEM_IMPL_EXPORT MojoResult
     PassWrappedPlatformHandle(MojoHandle platform_handle_wrapper_handle,
                               ScopedPlatformHandle* platform_handle);
 
 }  // namespace embedder
 }  // namespace mojo
 
 #endif  // MOJO_EMBEDDER_EMBEDDER_H_