Only draw the overhang pattern on overhang areas.

cc/trees/layer_tree_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_impl.h"
 
 #include "base/debug/trace_event.h"
 #include "cc/animation/keyframed_animation_curve.h"
 #include "cc/animation/scrollbar_animation_controller.h"
+#include "cc/base/math_util.h"
+#include "cc/base/util.h"
 #include "cc/debug/traced_value.h"
 #include "cc/layers/heads_up_display_layer_impl.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/render_surface_impl.h"
 #include "cc/layers/scrollbar_layer_impl_base.h"
 #include "cc/trees/layer_tree_host_common.h"
 #include "cc/trees/layer_tree_host_impl.h"
 #include "ui/gfx/size_conversions.h"
 #include "ui/gfx/vector2d_conversions.h"
 
@@ skipping 211 matching lines @@
     root_layer_scroll_offset_delegate_->SetTotalPageScaleFactor(
         total_page_scale_factor());
   }
 }
 
 gfx::SizeF LayerTreeImpl::ScrollableViewportSize() const {
   return gfx::ScaleSize(layer_tree_host_impl_->UnscaledScrollableViewportSize(),
                         1.0f / total_page_scale_factor());
 }
 
+gfx::Rect LayerTreeImpl::RootScrollLayerDeviceViewportBounds() const {
+  if (!root_scroll_layer_ || root_scroll_layer_->children().empty())
+    return gfx::Rect();
+  LayerImpl* layer = root_scroll_layer_->children()[0];
+  return MathUtil::MapClippedRect(
+      layer->screen_space_transform(),
+      gfx::Rect(layer->content_bounds()));
+}
+
 void LayerTreeImpl::UpdateMaxScrollOffset() {
   LayerImpl* root_scroll = RootScrollLayer();
   if (!root_scroll || !root_scroll->children().size())
     return;
 
   gfx::Vector2dF max_scroll = gfx::Rect(ScrollableSize()).bottom_right() -
       gfx::RectF(ScrollableViewportSize()).bottom_right();
 
   // The viewport may be larger than the contents in some cases, such as
   // having a vertical scrollbar but no horizontal overflow.
@@ skipping 514 matching lines @@
 const std::vector<LayerImpl*> LayerTreeImpl::LayersWithCopyOutputRequest()
     const {
   // Only the active tree needs to know about layers with copy requests, as
   // they are aborted if not serviced during draw.
   DCHECK(IsActiveTree());
 
   return layers_with_copy_output_request_;
 }
 
 }  // namespace cc