Fix spurious 1px scrolling.

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index e6e60f5f3ef7cc1e474c2b5c4a2aef192906b3b7..87cb2f8a8cfe4270a85f8abd9465b0c539a9a6fe 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -771,7 +771,7 @@ bool LayerImpl::IsActive() const {
 
 // TODO(wjmaclean) Convert so that bounds returns SizeF.

[danakj, 2014/08/20 17:00:25]

OT: A SizeF is going to be terrible for layers that are millions of pixels large
(think buildbot output), as the size of it will start to lose precision. Maybe
something else needs to be considered for this.

[aelias_OOO_until_Jul13, 2014/08/20 18:20:47]

The more serious issue is that layer bounds lack precision between DIPs.  This
is an underlying cause of this bug and also is a blocker for Android frontend UI
switching over to DIP coordinates.  I don't think the corner case of
8-million-pixel pages (I'm not sure even the buildbot pages are that long)
should be a greater concern, particularly since the floating point inaccuracy
would probably just cause minor rendering artifacts.  It doesn't seem worth
introducing fixed-point units just for this purpose either...

 gfx::Size LayerImpl::bounds() const {
-  return ToFlooredSize(temporary_impl_bounds_);
+  return ToCeiledSize(temporary_impl_bounds_);
 }
 
 void LayerImpl::SetBounds(const gfx::Size& bounds) {