Touchmoves should not be suppressed if the touchstart is consumed

third_party/WebKit/Source/core/input/TouchEventManager.cpp

 // Copyright 2016 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 "core/input/TouchEventManager.h"
 
 #include "core/dom/Document.h"
 #include "core/events/TouchEvent.h"
 #include "core/frame/Deprecation.h"
 #include "core/frame/EventHandlerRegistry.h"
@@ skipping 274 matching lines @@
                   ? HandledTouches
                   : UnhandledTouches);
         }
       }
       eventResult = EventHandlingUtil::mergeEventResult(
           eventResult,
           EventHandlingUtil::toWebInputEventResult(domDispatchResult));
     }
   }
 
+  if (m_suppressingTouchmovesWithinSlop &&
+      eventResult != WebInputEventResult::NotHandled) {

[mustaq, 2017/02/16 17:06:26]

This "!=NotHandled " applies only to touchstarts because in suppressed-state,
touchmoves can't be prevent-defaulted. Please add a comment here that this
applies only to touchstarts.

Also update the CL description accordingly.

[lanwei, 2017/02/16 19:48:59]

Done.

[mustaq, 2017/02/16 21:09:53]

Let me clarify a bit: this condition is met only for touchstarts, so we don't
need a new condition. Let's just add an ASSERT(event.type() ==
WebInputEvent::TouchStart) w/o any comments.

+    m_suppressingTouchmovesWithinSlop = false;
+  }
+
   return eventResult;
 }
 
 void TouchEventManager::updateTargetAndRegionMapsForTouchStarts(
     HeapVector<TouchInfo>& touchInfos) {
   for (auto& touchInfo : touchInfos) {
     // Touch events implicitly capture to the touched node, and don't change
     // active/hover states themselves (Gesture events do). So we only need
     // to hit-test on touchstart and when the target could be different than
     // the corresponding pointer event target.
@@ skipping 207 matching lines @@
   }
 
   return dispatchTouchEvents(event, touchInfos, allTouchesReleased);
 }
 
 bool TouchEventManager::isAnyTouchActive() const {
   return m_touchPressed;
 }
 
 }  // namespace blink