Send early ShowPress on TapDown when page isn't scrollable/pinchable.

Source/core/page/EventHandler.cpp

Index: Source/core/page/EventHandler.cpp
diff --git a/Source/core/page/EventHandler.cpp b/Source/core/page/EventHandler.cpp
index cf16660a6b045b4a2b1d4b08e4effbe9b3232974..ed9b6ba954c744a1baf86db945c2dd1148b10e20 100644
--- a/Source/core/page/EventHandler.cpp
+++ b/Source/core/page/EventHandler.cpp
@@ -2220,6 +2220,22 @@ void EventHandler::defaultWheelEventHandler(Node* startNode, WheelEvent* wheelEv
         m_previousWheelScrolledNode = stopNode;
 }
 
+bool EventHandler::hasScrollableAncestor(const Node* node) const

[Rick Byers, 2014/02/21 03:35:52]

some special cases that may require more general logic and test cases:
- <select> combo box
- <input> text field that has overflowed 
- is <textarea> the same as other overflow:scroll elements?
- a scrollable iframe without any other scrollable layers (I don't think the
root layers will have scrollsOverflow set true, will it?)

[bokan, 2014/02/24 14:55:35]

I'll also add list box (<select> with size < 5) to this list. I expect this to
be problematic since it handles scrolling in a rather unique way (no
RenderLayer, it itself is a ScrollableArea).

+{
+    RenderObject* renderer = node->renderer();
+
+    for (RenderLayer* parent = renderer ? renderer->enclosingLayer() : 0; parent; parent = parent->parent()) {

[Rick Byers, 2014/02/21 03:35:52]

Did bokan@ say that walking the layer tree was sufficient in all cases?  I
thought a normal <div style=overflow:scroll> wouldn't necessarily create a
layer...

[bokan, 2014/02/24 14:55:35]

I think (though I could be wrong) it'll always create a RenderLayer, just not a
CompositedLayerMapping. That said, I'd still suggest iterating over
RenderObjects rather than RenderLayers to avoid any surprises. In fact, it looks
like you shouldn't have to do this yourself: have a look at
RenderBox::canBeScrolledAndHasScrollableArea and
RenderObject::enclosingScrollableBox(), looks like it does exactly this.

+        if (parent->scrollsOverflow())
+            return true;
+    }
+
+    Frame* parent = m_frame->tree().parent();
+    if (!parent)
+        return false;
+
+    return parent->eventHandler().hasScrollableAncestor(m_frame->ownerElement());
+}
+
 bool EventHandler::handleGestureShowPress()
 {
     m_lastShowPressTimestamp = WTF::currentTime();
@@ -2244,36 +2260,9 @@ bool EventHandler::handleGestureShowPress()
 bool EventHandler::handleGestureEvent(const PlatformGestureEvent& gestureEvent)
 {
     IntPoint adjustedPoint = gestureEvent.position();
-    RefPtr<Frame> subframe = 0;
-    switch (gestureEvent.type()) {
-    case PlatformEvent::GestureScrollBegin:
-    case PlatformEvent::GestureScrollUpdate:
-    case PlatformEvent::GestureScrollUpdateWithoutPropagation:
-    case PlatformEvent::GestureScrollEnd:
-    case PlatformEvent::GestureFlingStart:
-        // Handle directly in main frame
-        break;
-
-    case PlatformEvent::GestureTap:
-    case PlatformEvent::GestureTapUnconfirmed:
-    case PlatformEvent::GestureTapDown:
-    case PlatformEvent::GestureShowPress:
-    case PlatformEvent::GestureTapDownCancel:
-    case PlatformEvent::GestureTwoFingerTap:
-    case PlatformEvent::GestureLongPress:
-    case PlatformEvent::GestureLongTap:
-    case PlatformEvent::GesturePinchBegin:
-    case PlatformEvent::GesturePinchEnd:
-    case PlatformEvent::GesturePinchUpdate:
-        adjustGesturePosition(gestureEvent, adjustedPoint);
-        subframe = getSubFrameForGestureEvent(adjustedPoint, gestureEvent);
-        if (subframe)
-            return subframe->eventHandler().handleGestureEvent(gestureEvent);
-        break;
-
-    default:
-        ASSERT_NOT_REACHED();
-    }
+    RefPtr<Frame> subframe = frameForGestureEvent(gestureEvent, adjustedPoint);
+    if (subframe != m_frame)
+        return subframe->eventHandler().handleGestureEvent(gestureEvent);
 
     Node* eventTarget = 0;
     Scrollbar* scrollbar = 0;
@@ -2650,13 +2639,44 @@ bool EventHandler::sendScrollEventToView(const PlatformGestureEvent& gestureEven
     return scrolledFrame;
 }
 
-Frame* EventHandler::getSubFrameForGestureEvent(const IntPoint& touchAdjustedPoint, const PlatformGestureEvent& gestureEvent)
+Frame* EventHandler::frameForGestureEvent(const PlatformGestureEvent& gestureEvent, IntPoint& adjustedPoint)
 {
-    PlatformMouseEvent mouseDown(touchAdjustedPoint, gestureEvent.globalPosition(), LeftButton, PlatformEvent::MousePressed, 1,
-        gestureEvent.shiftKey(), gestureEvent.ctrlKey(), gestureEvent.altKey(), gestureEvent.metaKey(), gestureEvent.timestamp());
-    HitTestRequest request(HitTestRequest::ReadOnly);
-    MouseEventWithHitTestResults mev = prepareMouseEvent(request, mouseDown);
-    return subframeForHitTestResult(mev);
+    switch (gestureEvent.type()) {
+    case PlatformEvent::GestureScrollBegin:
+    case PlatformEvent::GestureScrollUpdate:
+    case PlatformEvent::GestureScrollUpdateWithoutPropagation:
+    case PlatformEvent::GestureScrollEnd:
+    case PlatformEvent::GestureFlingStart:
+        // Handle in current frame
+        break;
+
+    case PlatformEvent::GestureTap:
+    case PlatformEvent::GestureTapUnconfirmed:
+    case PlatformEvent::GestureTapDown:
+    case PlatformEvent::GestureShowPress:
+    case PlatformEvent::GestureTapDownCancel:
+    case PlatformEvent::GestureTwoFingerTap:
+    case PlatformEvent::GestureLongPress:
+    case PlatformEvent::GestureLongTap:
+    case PlatformEvent::GesturePinchBegin:
+    case PlatformEvent::GesturePinchEnd:
+    case PlatformEvent::GesturePinchUpdate: {
+        adjustGesturePosition(gestureEvent, adjustedPoint);
+        PlatformMouseEvent mouseDown(adjustedPoint, gestureEvent.globalPosition(), LeftButton, PlatformEvent::MousePressed, 1,
+            gestureEvent.shiftKey(), gestureEvent.ctrlKey(), gestureEvent.altKey(), gestureEvent.metaKey(), gestureEvent.timestamp());
+        HitTestRequest request(HitTestRequest::ReadOnly);
+        MouseEventWithHitTestResults mev = prepareMouseEvent(request, mouseDown);
+        RefPtr<Frame> subframe = subframeForHitTestResult(mev);
+        if (subframe)
+            return subframe->eventHandler().frameForGestureEvent(gestureEvent, adjustedPoint);
+        break;
+    }
+
+    default:
+        ASSERT_NOT_REACHED();
+    }
+
+    return m_frame;
 }
 
 void EventHandler::clearGestureScrollNodes()