[POC; Not for Review] Don't use PostTask queueing between compositor and main thread.

content/renderer/input/input_event_filter.cc

Index: content/renderer/input/input_event_filter.cc
diff --git a/content/renderer/input/input_event_filter.cc b/content/renderer/input/input_event_filter.cc
index 109b4fe9ed029a4d005d4e0bbe96ff5ef64993ea..c0f59a16efa807504c42ebcdaa51dad482cee356 100644
--- a/content/renderer/input/input_event_filter.cc
+++ b/content/renderer/input/input_event_filter.cc
@@ -71,7 +71,8 @@ void InputEventFilter::SetIsFlingingInMainThreadEventQueue(int routing_id,
 void InputEventFilter::DidAddInputHandler(int routing_id) {
   base::AutoLock locked(routes_lock_);
   routes_.insert(routing_id);
-  route_queues_[routing_id].reset(new MainThreadEventQueue(routing_id, this));
+  route_queues_[routing_id].reset(new MainThreadEventQueue(
+      routing_id, this, main_listener_, main_task_runner_));
 }
 
 void InputEventFilter::DidRemoveInputHandler(int routing_id) {
@@ -229,7 +230,7 @@ void InputEventFilter::SendMessageOnIOThread(
   sender_->Send(message.release());
 }
 
-void InputEventFilter::SendEventToMainThread(
+void InputEventFilter::HandleEventOnMainThread(
     int routing_id,
     const blink::WebInputEvent* event,
     const ui::LatencyInfo& latency_info,
@@ -237,9 +238,11 @@ void InputEventFilter::SendEventToMainThread(
   TRACE_EVENT_INSTANT0(
       "input", "InputEventFilter::ForwardToHandler::SendEventToMainThread",
       TRACE_EVENT_SCOPE_THREAD);
+
   IPC::Message new_msg =
       InputMsg_HandleInputEvent(routing_id, event, latency_info, dispatch_type);
-  main_task_runner_->PostTask(FROM_HERE, base::Bind(main_listener_, new_msg));

[Sami, 2016/05/31 16:49:34]

Some of the logic in the renderer scheduler looks at pending work in the
input/compositing task queue (mainly [1]). If we're no longer posting tasks
there, that might cause us to miss some cases.

I *think* [1] isn't that useful anymore since most users have been converted
from yielding to using individual tasks. As long as we still call notifications
like DidHandleInputEventOnCompositorThread and DidHandleInputEventOnMainThread
the important cases should be covered.

[1]
https://code.google.com/p/chromium/codesearch#chromium/src/components/schedul...

[dtapuska, 2016/06/01 18:22:53]

We still are posting tasks; it just occurs at a different spot.

+
+  main_listener_.Run(new_msg);
 }
 
 }  // namespace content