Defer scroll status determination until scrolling has occurred

cc/trees/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/trees/layer_tree_host_impl.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/basictypes.h"
@@ skipping 1568 matching lines @@
   // contents of its texture are updated as the last thing before the frame is
   // drawn.
   if (active_tree_->hud_layer()) {
     TRACE_EVENT0("cc", "DrawLayers.UpdateHudTexture");
     active_tree_->hud_layer()->UpdateHudTexture(draw_mode,
                                                 resource_provider_.get());
   }
 
   if (draw_mode == DRAW_MODE_RESOURCELESS_SOFTWARE) {
     bool disable_picture_quad_image_filtering =
-        IsCurrentlyScrolling() || needs_animate_layers();
+        IsActivelyScrolling() || needs_animate_layers();
 
     scoped_ptr<SoftwareRenderer> temp_software_renderer =
         SoftwareRenderer::Create(this, &settings_, output_surface_.get(), NULL);
     temp_software_renderer->DrawFrame(&frame->render_passes,
                                       device_scale_factor_,
                                       DeviceViewport(),
                                       DeviceClip(),
                                       disable_picture_quad_image_filtering);
   } else {
     renderer_->DrawFrame(&frame->render_passes,
@@ skipping 161 matching lines @@
 }
 
 LayerImpl* LayerTreeHostImpl::OuterViewportScrollLayer() const {
   return active_tree_->OuterViewportScrollLayer();
 }
 
 LayerImpl* LayerTreeHostImpl::CurrentlyScrollingLayer() const {
   return active_tree_->CurrentlyScrollingLayer();
 }
 
-bool LayerTreeHostImpl::IsCurrentlyScrolling() const {
-  return CurrentlyScrollingLayer() ||
+bool LayerTreeHostImpl::IsActivelyScrolling() const {
+  return (did_lock_scrolling_layer_ && CurrentlyScrollingLayer()) ||
          (InnerViewportScrollLayer() &&
           InnerViewportScrollLayer()->IsExternalFlingActive()) ||
          (OuterViewportScrollLayer() &&
           OuterViewportScrollLayer()->IsExternalFlingActive());
 }
 
 // Content layers can be either directly scrollable or contained in an outer
 // scrolling layer which applies the scroll transform. Given a content layer,
 // this function returns the associated scroll layer if any.
 static LayerImpl* FindScrollLayerForContentLayer(LayerImpl* layer_impl) {
@@ skipping 1694 matching lines @@
 }
 
 void LayerTreeHostImpl::UnregisterPictureLayerImpl(PictureLayerImpl* layer) {
   std::vector<PictureLayerImpl*>::iterator it =
       std::find(picture_layers_.begin(), picture_layers_.end(), layer);
   DCHECK(it != picture_layers_.end());
   picture_layers_.erase(it);
 }
 
 }  // namespace cc