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

content/browser/renderer_host/render_process_host_impl.cc

Index: content/browser/renderer_host/render_process_host_impl.cc
diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index 9197d0ef769f132d3cae9633147f8e11e9effc8c..0d92caa9a6a1a89e1fe35beb1e6ac13457d18724 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -922,8 +922,7 @@ void RenderProcessHostImpl::NotifyTimezoneChange() {
 }
 
 ServiceRegistry* RenderProcessHostImpl::GetServiceRegistry() {
-  if (!mojo_application_host_)
-    return NULL;
+  DCHECK(mojo_application_host_);
   return mojo_application_host_->service_registry();
 }
 
@@ -1921,6 +1920,8 @@ void RenderProcessHostImpl::ProcessDied(bool already_dead) {
                     RenderProcessExited(this, GetHandle(), status, exit_code));
   within_process_died_observer_ = false;
 
+  mojo_application_host_->WillDestroySoon();
+
   child_process_launcher_.reset();
   channel_.reset();
   gpu_message_filter_ = NULL;
@@ -2023,6 +2024,8 @@ void RenderProcessHostImpl::OnShutdownRequest() {
       Source<RenderProcessHost>(this),
       NotificationService::NoDetails());
 
+  mojo_application_host_->WillDestroySoon();
+
   Send(new ChildProcessMsg_Shutdown());
 }