Don't use PostTask queueing between compositor and main thread.

content/browser/renderer_host/input/input_router_impl.cc

Index: content/browser/renderer_host/input/input_router_impl.cc
diff --git a/content/browser/renderer_host/input/input_router_impl.cc b/content/browser/renderer_host/input/input_router_impl.cc
index ab6ab3e5d40e55db4f257d9847b5ab8e3091ab49..e83bb5c6472749c31b065e090a0dbb3fdce09f60 100644
--- a/content/browser/renderer_host/input/input_router_impl.cc
+++ b/content/browser/renderer_host/input/input_router_impl.cc
@@ -79,7 +79,6 @@ InputRouterImpl::InputRouterImpl(IPC::Sender* sender,
       frame_tree_node_id_(-1),
       select_message_pending_(false),
       move_caret_pending_(false),
-      mouse_move_pending_(false),
       current_ack_source_(ACK_SOURCE_NONE),
       flush_requested_(false),
       active_renderer_fling_count_(0),
@@ -188,21 +187,8 @@ void InputRouterImpl::SendTouchEvent(
 // TouchpadTapSuppressionController.
 void InputRouterImpl::SendMouseEventImmediately(
     const MouseEventWithLatencyInfo& mouse_event) {
-  // Avoid spamming the renderer with mouse move events.  It is important
-  // to note that WM_MOUSEMOVE events are anyways synthetic, but since our
-  // thread is able to rapidly consume WM_MOUSEMOVE events, we may get way
-  // more WM_MOUSEMOVE events than we wish to send to the renderer.
-  if (mouse_event.event.type == WebInputEvent::MouseMove) {
-    if (mouse_move_pending_) {
-      if (!next_mouse_move_)
-        next_mouse_move_.reset(new MouseEventWithLatencyInfo(mouse_event));
-      else
-        next_mouse_move_->CoalesceWith(mouse_event);
-      return;
-    }
-    mouse_move_pending_ = true;
-    current_mouse_move_ = mouse_event;
-  }
+  if (mouse_event.event.type == blink::WebInputEvent::MouseMove)
+    mouse_move_queue_.push_back(mouse_event);

[tdresser, 2016/07/20 20:52:27]

Don't we still only need the most recent mousemove? Is a queue needed?

[dtapuska, 2016/07/27 05:29:00]

Unfortunately with the latency info we need to have the original event. We can
see if we can clean this code up but from my initial look is that it needs the
events to query a few fields like the latency input coordinates it adds to the
latency info object.

 
   FilterAndSendWebInputEvent(mouse_event.event, mouse_event.latency);
 }
@@ -243,7 +229,7 @@ void InputRouterImpl::RequestNotificationWhenFlushed() {
 
 bool InputRouterImpl::HasPendingEvents() const {
   return !touch_event_queue_.empty() || !gesture_event_queue_.empty() ||
-         !key_queue_.empty() || mouse_move_pending_ ||
+         !key_queue_.empty() || !mouse_move_queue_.empty() ||
          wheel_event_queue_.has_pending() || select_message_pending_ ||
          move_caret_pending_ || active_renderer_fling_count_ > 0;
 }
@@ -370,9 +356,6 @@ void InputRouterImpl::FilterAndSendWebInputEvent(
                          "step", "SendInputEventUI",
                          "frameTreeNodeId", frame_tree_node_id_);
 
-  // Any input event cancels a pending mouse move event.
-  next_mouse_move_.reset();
-
   OfferToHandlers(input_event, latency_info);
 }
 
@@ -408,7 +391,6 @@ bool InputRouterImpl::OfferToClient(const WebInputEvent& input_event,
     case INPUT_EVENT_ACK_STATE_CONSUMED:
     case INPUT_EVENT_ACK_STATE_NO_CONSUMER_EXISTS:
       // Send the ACK and early exit.
-      next_mouse_move_.reset();
       ProcessInputEventAck(
           input_event.type, filter_ack, latency_info,
           WebInputEventTraits::GetUniqueTouchEventId(input_event), CLIENT);
@@ -591,17 +573,13 @@ void InputRouterImpl::ProcessMouseAck(blink::WebInputEvent::Type type,
   if (type != WebInputEvent::MouseMove)
     return;
 
-  current_mouse_move_.latency.AddNewLatencyFrom(latency);
-  ack_handler_->OnMouseEventAck(current_mouse_move_, ack_result);
-
-  DCHECK(mouse_move_pending_);
-  mouse_move_pending_ = false;
-
-  if (next_mouse_move_) {
-    DCHECK(next_mouse_move_->event.type == WebInputEvent::MouseMove);
-    std::unique_ptr<MouseEventWithLatencyInfo> next_mouse_move =
-        std::move(next_mouse_move_);
-    SendMouseEvent(*next_mouse_move);
+  if (mouse_move_queue_.empty()) {
+    ack_handler_->OnUnexpectedEventAck(InputAckHandler::UNEXPECTED_ACK);
+  } else {
+    MouseEventWithLatencyInfo front_item = mouse_move_queue_.front();
+    front_item.latency.AddNewLatencyFrom(latency);
+    mouse_move_queue_.pop_front();
+    ack_handler_->OnMouseEventAck(front_item, ack_result);
   }
 }