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..5013e4d09e173c6b04a6bf72ac3621dc21ca74fe 100644
--- a/Source/platform/mac/ScrollElasticityController.mm
+++ b/Source/platform/mac/ScrollElasticityController.mm
@@ -99,6 +99,7 @@ static float scrollWheelMultiplier()
 ScrollElasticityController::ScrollElasticityController(ScrollElasticityControllerClient* client)
     : m_client(client)
     , m_inScrollGesture(false)
+    , m_hasScrolled(false)
     , m_momentumScrollInProgress(false)
     , m_ignoreMomentumScrolls(false)
     , m_lastMomentumScrollTimestamp(0)
@@ -109,13 +110,11 @@ ScrollElasticityController::ScrollElasticityController(ScrollElasticityControlle
 
 bool ScrollElasticityController::handleWheelEvent(const PlatformWheelEvent& wheelEvent)
 {
+    // When a new gesture begins, reset all state that might have been carried
+    // over from the last event.
     if (wheelEvent.phase() == PlatformWheelEventPhaseBegan) {
-        // First, check if we should rubber-band at all.
-        if (m_client->pinnedInDirection(FloatSize(-wheelEvent.deltaX(), 0)) &&
-            !shouldRubberBandInHorizontalDirection(wheelEvent))
-            return false;
-
         m_inScrollGesture = true;
+        m_hasScrolled = false;
         m_momentumScrollInProgress = false;
         m_ignoreMomentumScrolls = false;
         m_lastMomentumScrollTimestamp = 0;
@@ -128,10 +127,10 @@ bool ScrollElasticityController::handleWheelEvent(const PlatformWheelEvent& whee
 
         stopSnapRubberbandTimer();
 
-        return true;
+        return shouldHandleEvent(wheelEvent);
     }
 
-    if (wheelEvent.phase() == PlatformWheelEventPhaseEnded) {
+    if (wheelEvent.phase() == PlatformWheelEventPhaseEnded || wheelEvent.phase() == PlatformWheelEventPhaseCancelled) {

[erikchen, 2014/03/24 22:12:05]

this change wasn't necessary to make this CL work, but it appeared to be an
oversight from the original author. The phase PlatformWheelEventPhaseCancelled
is not mentioned anywhere in this file.

         bool wasRubberBandInProgress = isRubberBandInProgress();
         // Call snapRubberBand() even if isRubberBandInProgress() is false. For example,
         // m_inScrollGesture may be true (and needs to be reset on a phase end) even if
@@ -149,6 +148,9 @@ bool ScrollElasticityController::handleWheelEvent(const PlatformWheelEvent& whee
         return false;
     }
 
+    if (!shouldHandleEvent(wheelEvent))
+        return false;
+
     float deltaX = m_overflowScrollDelta.width();
     float deltaY = m_overflowScrollDelta.height();
 
@@ -241,6 +243,7 @@ bool ScrollElasticityController::handleWheelEvent(const PlatformWheelEvent& whee
     }
 
     if (deltaX != 0 || deltaY != 0) {
+        m_hasScrolled = true;
         if (!(shouldStretch || isVerticallyStretched || isHorizontallyStretched)) {
             if (deltaY != 0) {
                 deltaY *= scrollWheelMultiplier();
@@ -413,12 +416,17 @@ void ScrollElasticityController::snapRubberBand()
     m_snapRubberbandTimerIsActive = true;
 }
 
-bool ScrollElasticityController::shouldRubberBandInHorizontalDirection(const PlatformWheelEvent& wheelEvent)
+bool ScrollElasticityController::shouldHandleEvent(const PlatformWheelEvent& wheelEvent)
 {
-    if (wheelEvent.deltaX() > 0)
-        return m_client->shouldRubberBandInDirection(ScrollLeft);
-    if (wheelEvent.deltaX() < 0)
-        return m_client->shouldRubberBandInDirection(ScrollRight);
+    if (m_hasScrolled)
+        return true;
+    if (!m_client->pinnedInDirection(FloatSize(-wheelEvent.deltaX(), 0)))
+        return true;
+
+    if (wheelEvent.deltaX() > 0 && !wheelEvent.canRubberbandLeft())
+        return false;
+    if (wheelEvent.deltaX() < 0 && !wheelEvent.canRubberbandRight())
+        return false;
 
     return true;
 }