cc: Always commit and redraw after scrolling

cc/layer_tree_host_impl.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layer_tree_host_impl.h"
 
 #include <algorithm>
 
 #include "base/basictypes.h"
 #include "base/debug/trace_event.h"
@@ skipping 1274 matching lines @@
 }
 
 bool LayerTreeHostImpl::scrollBy(const gfx::Point& viewportPoint,
                                  const gfx::Vector2d& scrollDelta)
 {
     TRACE_EVENT0("cc", "LayerTreeHostImpl::scrollBy");
     if (!m_currentlyScrollingLayerImpl)
         return false;
 
     gfx::Vector2dF pendingDelta = scrollDelta;
+    bool didScroll = false;
 
     for (LayerImpl* layerImpl = m_currentlyScrollingLayerImpl; layerImpl; layerImpl = layerImpl->parent()) {
         if (!layerImpl->scrollable())
             continue;
 
         PinchZoomViewport* viewport = layerImpl == m_rootScrollLayerImpl ? &m_pinchZoomViewport : 0;
         gfx::Vector2dF appliedDelta;
         if (m_scrollDeltaIsInViewportSpace) {
             float scaleFromViewportToScreenSpace = m_deviceScaleFactor;
             appliedDelta = scrollLayerWithViewportSpaceDelta(viewport, *layerImpl, scaleFromViewportToScreenSpace, viewportPoint, pendingDelta);
         } else
             appliedDelta = scrollLayerWithLocalDelta(*layerImpl, pendingDelta);
 
         // If the layer wasn't able to move, try the next one in the hierarchy.
         float moveThresholdSquared = 0.1f * 0.1f;
         if (appliedDelta.LengthSquared() < moveThresholdSquared)
             continue;
+        didScroll = true;
 
         // If the applied delta is within 45 degrees of the input delta, bail out to make it easier
         // to scroll just one layer in one direction without affecting any of its parents.
         float angleThreshold = 45;
         if (MathUtil::smallestAngleBetweenVectors(appliedDelta, pendingDelta) < angleThreshold) {
             pendingDelta = gfx::Vector2d();
             break;
         }
 
         // Allow further movement only on an axis perpendicular to the direction in which the layer
         // moved.
         gfx::Vector2dF perpendicularAxis(-appliedDelta.y(), appliedDelta.x());
         pendingDelta = MathUtil::projectVector(pendingDelta, perpendicularAxis);
 
         if (gfx::ToFlooredVector2d(pendingDelta).IsZero())
             break;
     }
 
-    if (!scrollDelta.IsZero() && gfx::ToFlooredVector2d(pendingDelta).IsZero()) {
+    if (didScroll) {
         m_client->setNeedsCommitOnImplThread();
         m_client->setNeedsRedrawOnImplThread();
-        return true;
     }
-    return false;
+    return didScroll;
 }
 
 void LayerTreeHostImpl::clearCurrentlyScrollingLayer()
 {
     m_currentlyScrollingLayerImpl = 0;
     m_scrollingLayerIdFromPreviousTree = -1;
 }
 
 void LayerTreeHostImpl::scrollEnd()
 {
@@ skipping 285 matching lines @@
     ScrollbarAnimationController* scrollbarController = layer->scrollbarAnimationController();
     double monotonicTime = (time - base::TimeTicks()).InSecondsF();
     if (scrollbarController && scrollbarController->animate(monotonicTime))
         m_client->setNeedsRedrawOnImplThread();
 
     for (size_t i = 0; i < layer->children().size(); ++i)
         animateScrollbarsRecursive(layer->children()[i], time);
 }
 
 }  // namespace cc