Events ignoring ack disposition receive synthetic acks.

content/browser/renderer_host/input/immediate_input_router.cc

 // Copyright 2013 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/browser/renderer_host/input/immediate_input_router.h"
 
 #include "base/auto_reset.h"
 #include "base/command_line.h"
 #include "base/metrics/histogram.h"
 #include "content/browser/renderer_host/input/gesture_event_filter.h"
@@ skipping 322 matching lines @@
   if (input_event.type != WebInputEvent::MouseWheel) {
     for (size_t i = 0; i < coalesced_mouse_wheel_events_.size(); ++i) {
       SendWebInputEvent(coalesced_mouse_wheel_events_[i].event,
                         coalesced_mouse_wheel_events_[i].latency,
                         false);
     }
     coalesced_mouse_wheel_events_.clear();
   }
 
   SendWebInputEvent(input_event, latency_info, is_keyboard_shortcut);
+  // If we don't care about the ack disposition, send the ack immediately.
+  if (WebInputEventTraits::IgnoresAckDisposition(input_event.type)) {
+    ProcessInputEventAck(input_event.type,
+                         INPUT_EVENT_ACK_STATE_IGNORED,
+                         latency_info,
+                         CLIENT);

[jdduke (slow), 2013/10/25 20:53:34]

Please create a new enum entry for this ack source instead of repurposing
CLIENT.

[tdresser, 2013/11/04 15:57:30]

Done.

+  }
 
   // Any input event cancels a pending mouse move event.
   next_mouse_move_.reset();
 }
 
 bool ImmediateInputRouter::OfferToOverscrollController(
     const WebInputEvent& input_event,
     const ui::LatencyInfo& latency_info) {
   OverscrollController* controller = client_->GetOverscrollController();
   if (!controller)
@@ skipping 56 matching lines @@
 void ImmediateInputRouter::OnInputEventAck(
     WebInputEvent::Type event_type,
     InputEventAckState ack_result,
     const ui::LatencyInfo& latency_info) {
   // Log the time delta for processing an input event.
   TimeDelta delta = TimeTicks::Now() - input_event_start_time_;
   UMA_HISTOGRAM_TIMES("MPArch.IIR_InputEventDelta", delta);
 
   client_->DecrementInFlightEventCount();
 
+  // A synthetic ack will already have been sent for this event.
+  if (WebInputEventTraits::IgnoresAckDisposition(event_type))
+    return;
+
   ProcessInputEventAck(event_type, ack_result, latency_info, RENDERER);
   // WARNING: |this| may be deleted at this point.
 
   // This is used only for testing, and the other end does not use the
   // source object.  On linux, specifying
   // Source<RenderWidgetHost> results in a very strange
   // runtime error in the epilogue of the enclosing
   // (ProcessInputEventAck) method, but not on other platforms; using
   // 'void' instead is just as safe (since NotificationSource
   // is not actually typesafe) and avoids this error.
@@ skipping 238 matching lines @@
       break;
   }
 }
 
 bool ImmediateInputRouter::IsInOverscrollGesture() const {
   OverscrollController* controller = client_->GetOverscrollController();
   return controller && controller->overscroll_mode() != OVERSCROLL_NONE;
 }
 
 }  // namespace content