Fix recursion in handling touch input events acks.

content/browser/renderer_host/input/passthrough_touch_event_queue.cc

 // Copyright 2017 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/passthrough_touch_event_queue.h"
 
 #include <utility>
 
 #include "base/auto_reset.h"
 #include "base/macros.h"
@@ skipping 41 matching lines @@
   return event.unique_touch_event_id < other.event.unique_touch_event_id;
 }
 
 PassthroughTouchEventQueue::PassthroughTouchEventQueue(
     TouchEventQueueClient* client,
     const Config& config)
     : client_(client),
       has_handlers_(true),
       maybe_has_handler_for_current_sequence_(false),
       drop_remaining_touches_in_sequence_(false),
-      send_touch_events_async_(false) {
+      send_touch_events_async_(false),
+      processing_acks_(false) {
   if (config.touch_ack_timeout_supported) {
     timeout_handler_.reset(
         new TouchTimeoutHandler(this, config.desktop_touch_ack_timeout_delay,
                                 config.mobile_touch_ack_timeout_delay));
   }
 }
 
 PassthroughTouchEventQueue::~PassthroughTouchEventQueue() {}
 
 void PassthroughTouchEventQueue::SendTouchCancelEventForTouchEvent(
@@ skipping 125 matching lines @@
     auto iter = outstanding_touches_.begin();
     TouchEventWithLatencyInfoAndAckState event = *iter;
     outstanding_touches_.erase(iter);
     if (event.ack_state() == INPUT_EVENT_ACK_STATE_UNKNOWN)
       event.set_ack_state(INPUT_EVENT_ACK_STATE_NO_CONSUMER_EXISTS);
     AckTouchEventToClient(event, event.ack_state());
   }
 }
 
 void PassthroughTouchEventQueue::AckCompletedEvents() {
+  // Don't allow re-entrancy into this method otherwise
+  // the ordering of acks won't be preserved.
+  if (processing_acks_)
+    return;
+  base::AutoReset<bool> process_acks(&processing_acks_, true);
   while (!outstanding_touches_.empty()) {
     auto iter = outstanding_touches_.begin();
     if (iter->ack_state() == INPUT_EVENT_ACK_STATE_UNKNOWN)
       break;
     TouchEventWithLatencyInfoAndAckState event = *iter;
     outstanding_touches_.erase(iter);
     AckTouchEventToClient(event, event.ack_state());
   }
 }
 
@@ skipping 156 matching lines @@
 bool PassthroughTouchEventQueue::IsTimeoutRunningForTesting() const {
   return timeout_handler_ && timeout_handler_->IsTimeoutTimerRunning();
 }
 
 const TouchEventWithLatencyInfo&
 PassthroughTouchEventQueue::GetLatestEventForTesting() const {
   return *outstanding_touches_.rbegin();
 }
 
 }  // namespace content