Send the pending input event ack before the UpdateRect message

content/renderer/render_widget.cc

 // Copyright (c) 2011 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 "content/renderer/render_widget.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
@@ skipping 463 matching lines @@
   const WebInputEvent* input_event =
       reinterpret_cast<const WebInputEvent*>(data);
 
   bool is_keyboard_shortcut = false;
   // is_keyboard_shortcut flag is only available for RawKeyDown events.
   if (input_event->type == WebInputEvent::RawKeyDown)
     message.ReadBool(&iter, &is_keyboard_shortcut);
 
   bool prevent_default = false;
   if (WebInputEvent::isMouseEventType(input_event->type)) {
-    prevent_default = WillHandleMouseEvent(
-        *(static_cast<const WebMouseEvent*>(input_event)));
+    const WebMouseEvent& mouse_event =
+        *static_cast<const WebMouseEvent*>(input_event);
+    TRACE_EVENT2("renderer", "HandleMouseMove",
+                 "x", mouse_event.x, "y", mouse_event.y);
+    prevent_default = WillHandleMouseEvent(mouse_event);
   }
 
   bool processed = prevent_default;
   if (input_event->type != WebInputEvent::Char || !suppress_next_char_events_) {
     suppress_next_char_events_ = false;
     if (!processed && webwidget_)
       processed = webwidget_->handleInputEvent(*input_event);
   }
 
   // If this RawKeyDown event corresponds to a browser keyboard shortcut and
@@ skipping 376 matching lines @@
     // rects to save the browser process from doing unecessary work.
     pending_update_params_->bitmap_rect = bounds;
     pending_update_params_->scroll_rect = gfx::Rect();
     // We don't need an ack, because we're not sharing a DIB with the browser.
     // If it needs to (e.g. composited UI), the GPU process does its own ACK
     // with the browser for the GPU surface.
     pending_update_params_->needs_ack = false;
     webwidget_->composite(false);
   }
 
+  // If we're holding a pending input event ACK, send the ACK before sending the
+  // UpdateReply message so we can receive another input event before the
+  // UpdateRect_ACK on platforms where the UpdateRect_ACK is sent from within
+  // the UpdateRect IPC message handler.
+  if (pending_input_event_ack_.get())
+    Send(pending_input_event_ack_.release());
+
   // If composite() called SwapBuffers, pending_update_params_ will be reset (in
   // OnSwapBuffersPosted), meaning a message has been added to the
   // updates_pending_swap_ queue, that will be sent later. Otherwise, we send
   // the message now.
   if (pending_update_params_.get()) {
     // sending an ack to browser process that the paint is complete...
     update_reply_pending_ = pending_update_params_->needs_ack;
     Send(new ViewHostMsg_UpdateRect(routing_id_, *pending_update_params_));
     pending_update_params_.reset();
   }
@@ skipping 651 matching lines @@
   }
 }
 
 bool RenderWidget::WillHandleMouseEvent(const WebKit::WebMouseEvent& event) {
   return false;
 }
 
 bool RenderWidget::WebWidgetHandlesCompositorScheduling() const {
   return false;
 }