Mark touchcancel events as uncancelable

content/browser/renderer_host/input/input_router_impl.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/input_router_impl.h"
 
 #include "base/auto_reset.h"
 #include "base/command_line.h"
 #include "base/metrics/histogram.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 428 matching lines @@
   }
 
   if (OfferToOverscrollController(input_event, latency_info))
     return;
 
   if (OfferToClient(input_event, latency_info))
     return;
 
   OfferToRenderer(input_event, latency_info, is_keyboard_shortcut);
 
+  // Touch events should always indicate in the event whether they are
+  // cancelable (respect ACK disposition) or not.
+  bool ignoresAck =
+      WebInputEventTraits::IgnoresAckDisposition(input_event.type);
+  if (WebInputEvent::isTouchEventType(input_event.type)) {
+    DCHECK(!ignoresAck ==
+        static_cast<const blink::WebTouchEvent&>(input_event).cancelable);
+  }
+
   // If we don't care about the ack disposition, send the ack immediately.
-  if (WebInputEventTraits::IgnoresAckDisposition(input_event.type)) {
+  if (ignoresAck) {
     ProcessInputEventAck(input_event.type,
                          INPUT_EVENT_ACK_STATE_IGNORED,
                          latency_info,
                          IGNORING_DISPOSITION);
   }
 }
 
 bool InputRouterImpl::OfferToOverscrollController(
     const WebInputEvent& input_event,
     const ui::LatencyInfo& latency_info) {
@@ skipping 388 matching lines @@
          select_range_pending_ ||
          move_caret_pending_;
 }
 
 bool InputRouterImpl::IsInOverscrollGesture() const {
   OverscrollController* controller = client_->GetOverscrollController();
   return controller && controller->overscroll_mode() != OVERSCROLL_NONE;
 }
 
 }  // namespace content