Use WaitableEvents to wake up sync IPC waiting

ipc/ipc_sync_message_filter.h

Index: ipc/ipc_sync_message_filter.h
diff --git a/ipc/ipc_sync_message_filter.h b/ipc/ipc_sync_message_filter.h
index abee662db3c501d09ad2a1855ddeb098bdd4fedd..17ec5297aa12c6052cd3bb650e06a308f878cbc3 100644
--- a/ipc/ipc_sync_message_filter.h
+++ b/ipc/ipc_sync_message_filter.h
@@ -10,13 +10,10 @@
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
-#include "base/memory/weak_ptr.h"
 #include "base/synchronization/lock.h"
-#include "base/synchronization/waitable_event_watcher.h"
 #include "ipc/ipc_sender.h"
 #include "ipc/ipc_sync_message.h"
 #include "ipc/message_filter.h"
-#include "ipc/mojo_event.h"
 #include "mojo/public/cpp/bindings/associated_interface_ptr.h"
 #include "mojo/public/cpp/bindings/associated_interface_request.h"
 #include "mojo/public/cpp/bindings/scoped_interface_endpoint_handle.h"
@@ -63,18 +60,12 @@ class IPC_EXPORT SyncMessageFilter : public MessageFilter, public Sender {
   ~SyncMessageFilter() override;
 
  private:
-  class IOMessageLoopObserver;
-
   friend class SyncChannel;
-  friend class IOMessageLoopObserver;
 
   void SendOnIOThread(Message* message);
   // Signal all the pending sends as done, used in an error condition.
   void SignalAllEvents();
 
-  void OnShutdownEventSignaled(base::WaitableEvent* event);
-  void OnIOMessageLoopDestroyed();
-
   // NOTE: This must ONLY be called on the Channel's thread.
   void GetGenericRemoteAssociatedInterface(
       const std::string& interface_name,
@@ -100,18 +91,6 @@ class IPC_EXPORT SyncMessageFilter : public MessageFilter, public Sender {
 
   base::WaitableEvent* const shutdown_event_;
 
-  // Used to asynchronously watch |shutdown_event_| on the IO thread and forward
-  // to |shutdown_mojo_event_| (see below.)
-  base::WaitableEventWatcher shutdown_watcher_;
-
-  // A Mojo event which can be watched for shutdown. Signals are forwarded to
-  // this event asynchronously from |shutdown_event_|.
-  MojoEvent shutdown_mojo_event_;
-
-  scoped_refptr<IOMessageLoopObserver> io_message_loop_observer_;
-
-  base::WeakPtrFactory<SyncMessageFilter> weak_factory_;
-
   DISALLOW_COPY_AND_ASSIGN(SyncMessageFilter);
 };