Revert "Send input event IPCs directly from the UI thread"

ipc/mojo/ipc_channel_mojo.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 "ipc/mojo/ipc_channel_mojo.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
@@ skipping 360 matching lines @@
 
   if (!sent) {
     OnPipeError();
     return false;
   }
 
   return true;
 }
 
 bool ChannelMojo::IsSendThreadSafe() const {
-  return true;
+  return false;
 }
 
 base::ProcessId ChannelMojo::GetPeerPID() const {
   base::AutoLock lock(lock_);
   if (!message_reader_)
     return base::kNullProcessId;
 
   return message_reader_->GetPeerPid();
 }
 
@@ skipping 71 matching lines @@
     DCHECK(ok);
     if (!ok) {
       LOG(ERROR) << "Failed to add new Mojo handle.";
       return MOJO_RESULT_UNKNOWN;
     }
   }
   return MOJO_RESULT_OK;
 }
 
 }  // namespace IPC