Notify Blink about start of gesture scroll through a queued event.

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

Index: third_party/WebKit/Source/core/input/EventHandler.cpp
diff --git a/third_party/WebKit/Source/core/input/EventHandler.cpp b/third_party/WebKit/Source/core/input/EventHandler.cpp
index faa7a4369530259eafb0876798511dcbeacb75cf..69ab4aaf310a4cfcdd2f5fe274b9b0b84a6aec6d 100644
--- a/third_party/WebKit/Source/core/input/EventHandler.cpp
+++ b/third_party/WebKit/Source/core/input/EventHandler.cpp
@@ -259,7 +259,6 @@ EventHandler::EventHandler(LocalFrame* frame)
     , m_mousePositionIsUnknown(true)
     , m_mouseDownTimestamp(0)
     , m_touchPressed(false)
-    , m_inPointerCanceledState(false)
     , m_scrollGestureHandlingNode(nullptr)
     , m_lastGestureScrollOverWidget(false)
     , m_longTapShouldInvokeContextMenu(false)
@@ -336,7 +335,6 @@ void EventHandler::clear()
     m_scrollbarHandlingScrollGesture = nullptr;
     m_touchPressed = false;
     m_pointerEventManager.clear();
-    m_inPointerCanceledState = false;
     m_mouseDownMayStartDrag = false;
     m_lastShowPressTimestamp = 0;
     m_lastDeferredTapElement = nullptr;
@@ -3590,26 +3588,6 @@ void EventHandler::dispatchPointerEvents(const PlatformTouchEvent& event,
     }
 }
 
-void EventHandler::sendPointerCancels(WillBeHeapVector<TouchInfo>& touchInfos)
-{
-    if (!RuntimeEnabledFeatures::pointerEventEnabled())
-        return;
-
-    for (unsigned i = 0; i < touchInfos.size(); ++i) {
-        TouchInfo& touchInfo = touchInfos[i];
-        const PlatformTouchPoint& point = touchInfo.point;
-        const PlatformTouchPoint::TouchState pointState = point.state();
-
-        if (pointState == PlatformTouchPoint::TouchReleased
-            || pointState == PlatformTouchPoint::TouchCancelled)
-            continue;
-
-        m_pointerEventManager.sendTouchCancelPointerEvent(
-            touchInfo.touchTarget,
-            point);
-    }
-}
-
 namespace {
 
 // Defining this class type local to dispatchTouchEvents() and annotating
@@ -3733,6 +3711,11 @@ WebInputEventResult EventHandler::handleTouchEvent(const PlatformTouchEvent& eve
 {
     TRACE_EVENT0("blink", "EventHandler::handleTouchEvent");
 
+    if (event.type() == PlatformEvent::TouchScrollStarted) {
+        m_pointerEventManager.blockTouchPointers();
+        return WebInputEventResult::HandledSystem;
+    }
+
     const Vector<PlatformTouchPoint>& points = event.touchPoints();
 
     bool freshTouchEvents = true;

[tdresser, 2016/04/01 14:50:24]

I'm not a big fan of the name of this variable. Could we rename it to something
like "startingNewTouchSequence"?

[mustaq, 2016/04/01 18:31:05]

Done.

@@ -3909,33 +3892,19 @@ WebInputEventResult EventHandler::handleTouchEvent(const PlatformTouchEvent& eve
         touchInfo.region = regionID;
     }
 
-    if (!m_inPointerCanceledState) {
-        dispatchPointerEvents(event, touchInfos);
-        // Note that the disposition of any pointer events affects only the generation of touch
-        // events. If all pointer events were handled (and hence no touch events were fired), that
-        // is still equivalent to the touch events going unhandled because pointer event handler
-        // don't block scroll gesture generation.
-    }
+    if (freshTouchEvents)
+        m_pointerEventManager.unblockTouchPointers();
+    dispatchPointerEvents(event, touchInfos);
+    // Note that the disposition of any pointer events affects only the generation of touch
+    // events. If all pointer events were handled (and hence no touch events were fired), that
+    // is still equivalent to the touch events going unhandled because pointer event handler
+    // don't block scroll gesture generation.
 
     // TODO(crbug.com/507408): If PE handlers always call preventDefault, we won't see TEs until after
     // scrolling starts because the scrolling would suppress upcoming PEs. This sudden "break" in TE
     // suppression can make the visible TEs inconsistent (e.g. touchmove without a touchstart).
 
-    WebInputEventResult eventResult = dispatchTouchEvents(event, touchInfos, freshTouchEvents,
-        allTouchReleased);
-
-    if (!m_inPointerCanceledState) {
-        // Check if we need to stop firing pointer events because of a touch action.
-        // See: www.w3.org/TR/pointerevents/#declaring-candidate-regions-for-default-touch-behaviors
-        if (event.causesScrollingIfUncanceled() && eventResult == WebInputEventResult::NotHandled) {
-            m_inPointerCanceledState = true;
-            sendPointerCancels(touchInfos);
-        }
-    } else if (allTouchReleased) {
-        m_inPointerCanceledState = false;
-    }
-
-    return eventResult;
+    return dispatchTouchEvents(event, touchInfos, freshTouchEvents, allTouchReleased);
 }
 
 void EventHandler::setLastKnownMousePosition(const PlatformMouseEvent& event)