Selectively disable rubber banding on mac.

Source/platform/mac/ScrollElasticityController.mm

Index: Source/platform/mac/ScrollElasticityController.mm
diff --git a/Source/platform/mac/ScrollElasticityController.mm b/Source/platform/mac/ScrollElasticityController.mm
index 0ab305b6ab91823e3ff09e4e30feebf082a77ac4..65a9ea82db70f24657cf5dd78b7f19f7179b6a95 100644
--- a/Source/platform/mac/ScrollElasticityController.mm
+++ b/Source/platform/mac/ScrollElasticityController.mm
@@ -110,9 +110,7 @@ ScrollElasticityController::ScrollElasticityController(ScrollElasticityControlle
 bool ScrollElasticityController::handleWheelEvent(const PlatformWheelEvent& wheelEvent)
 {
     if (wheelEvent.phase() == PlatformWheelEventPhaseBegan) {
-        // First, check if we should rubber-band at all.
-        if (m_client->pinnedInDirection(FloatSize(-wheelEvent.deltaX(), 0)) &&
-            !shouldRubberBandInHorizontalDirection(wheelEvent))
+        if (!shouldStartRubberBanding(wheelEvent))
             return false;
 
         m_inScrollGesture = true;
@@ -185,6 +183,9 @@ bool ScrollElasticityController::handleWheelEvent(const PlatformWheelEvent& whee
 
     // If we are starting momentum scrolling then do some setup.
     if (!m_momentumScrollInProgress && (momentumPhase == PlatformWheelEventPhaseBegan || momentumPhase == PlatformWheelEventPhaseChanged)) {
+        if (!shouldStartRubberBanding(wheelEvent))
+            return false;
+
         m_momentumScrollInProgress = true;
         // Start the snap rubber band timer if it's not running. This is needed to
         // snap back from the over scroll caused by momentum events.
@@ -413,12 +414,22 @@ void ScrollElasticityController::snapRubberBand()
     m_snapRubberbandTimerIsActive = true;
 }
 
-bool ScrollElasticityController::shouldRubberBandInHorizontalDirection(const PlatformWheelEvent& wheelEvent)
+bool ScrollElasticityController::shouldStartRubberBanding(const PlatformWheelEvent& wheelEvent)
 {
-    if (wheelEvent.deltaX() > 0)
-        return m_client->shouldRubberBandInDirection(ScrollLeft);
-    if (wheelEvent.deltaX() < 0)
-        return m_client->shouldRubberBandInDirection(ScrollRight);
+    if (wheelEvent.deltaX() > 0) {
+        if (!wheelEvent.canRubberbandLeft())
+            return false;
+        if (m_client->pinnedInDirection(FloatSize(-wheelEvent.deltaX(), 0)) && !m_client->shouldRubberBandInDirection(ScrollLeft))

[Alexei Svitkine (slow), 2014/03/20 18:38:09]

Could the pinnedInDirection() check be made inside
m_client->shouldRubberBandInDirection() so two calls aren't required here?

[erikchen, 2014/03/24 22:12:04]

I've reworked the logic of this method to be much simpler.
m_client->shouldRubberBandInDirection() is no longer used - see my comment in
the header file and the CL description.

+            return false;
+        return true;
+    }
+    if (wheelEvent.deltaX() < 0) {
+        if (!wheelEvent.canRubberbandRight())
+            return false;
+        if (m_client->pinnedInDirection(FloatSize(-wheelEvent.deltaX(), 0)) && !m_client->shouldRubberBandInDirection(ScrollRight))
+            return false;
+        return true;
+    }
 
     return true;
 }