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_)
+    return gfx::Rect();
+  return MathUtil::MapClippedRect(
+      root_scroll_layer_->screen_space_transform(),
+      gfx::Rect(root_scroll_layer_->content_bounds()));

[enne (OOO), 2013/11/05 01:05:17]

I think this should do the same thing as ScrollableSize, aka
root_scroll_layer_->children()[0].

If it's the case that the root scroll layer is always sized correctly, then we
should just use the root_scroll_layer_->bounds() in ScrollableSize too.

(aelias, do you remember what the state of this is?)

[aelias_OOO_until_Jul13, 2013/11/05 01:15:18]

As far as I know, the Blink bug causing that to occasionally be empty is still
not fixed (unless it went away on its own in the general Blink churn).  It would
be better to call ScrollableSize() here.  But even better would be to use
RootContainerLayer().bounds() I think?  Those would not need to be transformed.

[ccameron, 2013/11/05 01:15:20]

Okay -- updated to use root scroll layer's first child. It seemed to be the
right size when I looked at it.

+}
+
 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