Respect the order of input messages from browser to renderer

content/renderer/input/input_handler_manager.cc

Index: content/renderer/input/input_handler_manager.cc
diff --git a/content/renderer/input/input_handler_manager.cc b/content/renderer/input/input_handler_manager.cc
index b6deb4c0b187c2064f916160e10aa46aff04cebb..52df5f63931de3c502e1d0117c71d59e6927c67a 100644
--- a/content/renderer/input/input_handler_manager.cc
+++ b/content/renderer/input/input_handler_manager.cc
@@ -107,7 +107,7 @@ void InputHandlerManager::AddInputHandlerOnCompositorThread(
   std::unique_ptr<InputHandlerWrapper> wrapper(new InputHandlerWrapper(
       this, routing_id, main_task_runner, input_handler, render_view_impl,
       enable_smooth_scrolling, enable_wheel_gestures));
-  client_->DidAddInputHandler(routing_id);
+  client_->RegisterRoutingID(routing_id);
   if (synchronous_handler_proxy_client_) {
     synchronous_handler_proxy_client_->DidAddSynchronousHandlerProxy(
         routing_id, wrapper->input_handler_proxy());
@@ -121,7 +121,7 @@ void InputHandlerManager::RemoveInputHandler(int routing_id) {
 
   TRACE_EVENT0("input", "InputHandlerManager::RemoveInputHandler");
 
-  client_->DidRemoveInputHandler(routing_id);
+  client_->UnregisterRoutingID(routing_id);
   if (synchronous_handler_proxy_client_) {
     synchronous_handler_proxy_client_->DidRemoveSynchronousHandlerProxy(
         routing_id);
@@ -129,6 +129,21 @@ void InputHandlerManager::RemoveInputHandler(int routing_id) {
   input_handlers_.erase(routing_id);
 }
 
+void InputHandlerManager::RegisterRoutingID(int routing_id) {
+  if (task_runner_->BelongsToCurrentThread()) {
+    RegisterRoutingIDOnCompositorThread(routing_id);
+  } else {
+    task_runner_->PostTask(
+        FROM_HERE,
+        base::Bind(&InputHandlerManager::RegisterRoutingIDOnCompositorThread,
+                   base::Unretained(this), routing_id));
+  }
+}
+
+void InputHandlerManager::RegisterRoutingIDOnCompositorThread(int routing_id) {
+  client_->RegisterRoutingID(routing_id);
+}
+
 void InputHandlerManager::ObserveWheelEventAndResultOnMainThread(
     int routing_id,
     const blink::WebMouseWheelEvent& wheel_event,