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));
     }
   }
 
+  // Do not suppress any touchmoves if the touchstart is consumed.

[Rick Byers, 2017/02/16 21:21:57]

nit: it seems like it would be a small clean-up to move the
"m_suppressingTouchmovesWithinSlop = true;" line down from 131 into here.  I.e.
instead of setting it and then clearing it, we could just ONLY set it after a
touchstart has been dispatched that wasn't cancelled.

[mustaq, 2017/02/16 21:41:26]

The "true" value is used in Line 138, so we have to leave things up there
anyways I think.

[Rick Byers, 2017/02/16 22:09:19]

But it's used only if we're currently processing a TouchMove, and here we're
talking about setting it only after a TouchStart.  I.e. "am I suppressing slop
moves" is relevant between the time AFTER a the first touchstart has been
dispatched up until just BEFORE the last touchend/cancel has been dispatched. 
This bit doesn't really make sense DURING the dispatch of the first touchstart -
we don't actually know yet if we should be suppressing slop movement or not (and
it's irrelevant until we get the first move anyway).

[lanwei, 2017/02/17 15:11:17]

Acknowledged.
Yes, we can merge line 131 here, thank you.

+  if (m_suppressingTouchmovesWithinSlop &&
+      event.type() == WebInputEvent::TouchStart &&
+      eventResult != WebInputEventResult::NotHandled) {
+    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