Only draw the overhang pattern on overhang areas.

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 4604043663920750438b5de260b0d8a0249d36b2..1ba1609c2c82f3b9e175a555f9844ac066d4e131 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -7,6 +7,8 @@
 #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"
@@ -238,6 +240,14 @@ gfx::SizeF LayerTreeImpl::ScrollableViewportSize() const {
                         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())