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

mojo/embedder/channel_init.h

Index: mojo/embedder/channel_init.h
diff --git a/mojo/embedder/channel_init.h b/mojo/embedder/channel_init.h
index d06332f1db68f45c91af2ef6de76160eb9c078b6..00337c5f0043a9befdfb67ed83d5e7962296f4e8 100644
--- a/mojo/embedder/channel_init.h
+++ b/mojo/embedder/channel_init.h
@@ -23,8 +23,8 @@ struct ChannelInfo;
 
 namespace embedder {
 
-// ChannelInit handle creation (and destruction) of the mojo channel. It is
-// expected that this class is created and destroyed on the main thread.
+// |ChannelInit| handles creation (and destruction) of the Mojo channel. It is
+// not thread-safe, but may be used on any single thread (with a |MessageLoop|).
 class MOJO_SYSTEM_IMPL_EXPORT ChannelInit {
  public:
   ChannelInit();
@@ -36,9 +36,14 @@ class MOJO_SYSTEM_IMPL_EXPORT ChannelInit {
       base::PlatformFile file,
       scoped_refptr<base::TaskRunner> io_thread_task_runner);
 
+  // Notifies the channel that we (hence it) will soon be destroyed.
+  void WillDestroySoon();
+
  private:
-  // Invoked on the main thread once the channel has been established.
-  static void OnCreatedChannel(base::WeakPtr<ChannelInit> host,
+  // Invoked on the thread on which this object lives once the channel has been
+  // established. (This is a static method that takes a weak pointer to self,
+  // since we want to destroy the channel even if we're destroyed.)
+  static void OnCreatedChannel(base::WeakPtr<ChannelInit> self,
                                scoped_refptr<base::TaskRunner> io_thread,
                                embedder::ChannelInfo* channel);