Implement one-page-at-a-time mousewheel scrolling in the impl thread.

cc/layer.cc

 // Copyright 2010 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.h"
 
 #include "cc/animation.h"
 #include "cc/animation_events.h"
 #include "cc/layer_animation_controller.h"
 #include "cc/layer_impl.h"
@@ skipping 434 matching lines @@
 }
 
 void Layer::setMaxScrollOffset(gfx::Vector2d maxScrollOffset)
 {
     if (m_maxScrollOffset == maxScrollOffset)
         return;
     m_maxScrollOffset = maxScrollOffset;
     setNeedsCommit();
 }
 
+void Layer::setVisibleScrollArea(gfx::Size visibleScrollArea)
+{
+    if (m_visibleScrollArea == visibleScrollArea)
+        return;
+    m_visibleScrollArea = visibleScrollArea;
+    setNeedsCommit();
+}
+
+
 void Layer::setScrollable(bool scrollable)
 {
     if (m_scrollable == scrollable)
         return;
     m_scrollable = scrollable;
     setNeedsCommit();
 }
 
 void Layer::setShouldScrollOnMainThread(bool shouldScrollOnMainThread)
 {
@@ skipping 141 matching lines @@
     layer->setFixedToContainerLayer(m_fixedToContainerLayer);
     layer->setPreserves3D(preserves3D());
     layer->setUseParentBackfaceVisibility(m_useParentBackfaceVisibility);
     layer->setSublayerTransform(m_sublayerTransform);
     if (!transformIsAnimating())
         layer->setTransform(m_transform);
 
     layer->setScrollable(m_scrollable);
     layer->setScrollOffset(m_scrollOffset);
     layer->setMaxScrollOffset(m_maxScrollOffset);
+    layer->setVisibleScrollArea(m_visibleScrollArea);
 
     // If the main thread commits multiple times before the impl thread actually draws, then damage tracking
     // will become incorrect if we simply clobber the updateRect here. The LayerImpl's updateRect needs to
     // accumulate (i.e. union) any update changes that have occurred on the main thread.
     m_updateRect.Union(layer->updateRect());
     layer->setUpdateRect(m_updateRect);
 
     if (layer->layerTreeImpl()->settings().implSidePainting) {
         DCHECK(layer->layerTreeImpl()->IsPendingTree());
         LayerImpl* active_twin = layer->layerTreeImpl()->FindActiveTreeLayerById(id());
@@ skipping 224 matching lines @@
 {
     return 0;
 }
 
 void sortLayers(std::vector<scoped_refptr<Layer> >::iterator, std::vector<scoped_refptr<Layer> >::iterator, void*)
 {
     // Currently we don't use z-order to decide what to paint, so there's no need to actually sort Layers.
 }
 
 }  // namespace cc