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 8bff7ef00ce8fca1468a1e57c20cb5ede056c20e..e9fa0e9baadd834c7dc6e5682e93c61fe31b3b20 100644
--- a/Source/core/page/EventHandler.cpp
+++ b/Source/core/page/EventHandler.cpp
@@ -2220,6 +2220,30 @@ void EventHandler::defaultWheelEventHandler(Node* startNode, WheelEvent* wheelEv
         m_previousWheelScrolledNode = stopNode;
 }
 
+bool EventHandler::hasScrollableAncestor(const Node* node) const
+{
+    RenderObject* renderer = node->renderer();
+    while (node && !renderer) {
+        node = node->parentElement();
+        renderer = node ? node->renderer() : 0;
+    }
+
+    if (renderer && renderer->isBox()) {
+        RenderBox* box = toRenderBox(renderer);
+        if (box->canBeScrolledAndHasScrollableArea())
+            return true;
+    }
+
+    if (renderer && renderer->enclosingScrollableBox())
+        return true;
+
+    LocalFrame* 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 +2268,9 @@ bool EventHandler::handleGestureShowPress()
 bool EventHandler::handleGestureEvent(const PlatformGestureEvent& gestureEvent)
 {
     IntPoint adjustedPoint = gestureEvent.position();
-    RefPtr<LocalFrame> subframe = nullptr;
-    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<LocalFrame> subframe = frameForGestureEvent(gestureEvent, adjustedPoint);
+    if (subframe != m_frame)
+        return subframe->eventHandler().handleGestureEvent(gestureEvent);
 
     Node* eventTarget = 0;
     Scrollbar* scrollbar = 0;
@@ -2650,13 +2647,44 @@ bool EventHandler::sendScrollEventToView(const PlatformGestureEvent& gestureEven
     return scrolledFrame;
 }
 
-LocalFrame* EventHandler::getSubFrameForGestureEvent(const IntPoint& touchAdjustedPoint, const PlatformGestureEvent& gestureEvent)
+LocalFrame* 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:

[Rick Byers, 2014/03/13 01:40:06]

I know you're just moving code around here, but this division feels odd to me. 
Ideally we'd have a comment saying how we decided which should be handled in the
current frame and which need adjustment down to the subframe.  Eg. pinch should
probably be handled in the same way as scroll (although I don't think we
actually receive pinch events in WebCore).

[Zeeshan Qureshi, 2014/03/24 21:37:43]

I'm not quite sure why, I was hoping to dig into it when continuing work on
http://crrev.com/130433009 as it will require modifying a good chunk of
EventHandler::handleGestureEvent().

[Rick Byers, 2014/03/25 19:46:47]

Ok, deferring this to a future CL is fine.  Thanks.

+    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<LocalFrame> subframe = subframeForHitTestResult(mev);
+        if (subframe)
+            return subframe->eventHandler().frameForGestureEvent(gestureEvent, adjustedPoint);
+        break;
+    }
+
+    default:
+        ASSERT_NOT_REACHED();
+    }
+
+    return m_frame;
 }
 
 void EventHandler::clearGestureScrollNodes()