Make tile size a function of the device scale factor.

cc/trees/layer_tree_impl.h

Index: cc/trees/layer_tree_impl.h
diff --git a/cc/trees/layer_tree_impl.h b/cc/trees/layer_tree_impl.h
index dadc6c3d3a2fcf8ab75624c6b831410a7cb28566..b6569c42009af2a51e6ddb1d515123155be6e7d6 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -105,7 +105,8 @@ class CC_EXPORT LayerTreeImpl {
   base::TimeDelta CurrentBeginFrameInterval() const;
   gfx::Rect DeviceViewport() const;
   gfx::Size DrawViewportSize() const;
-  const gfx::Rect ViewportRectForTilePriority() const;
+  gfx::Size GetStableScreenSize() const;

[aelias_OOO_until_Jul13, 2016/06/29 07:21:16]

Hmm, any reason you decided not to use OutputSurface::SurfaceSize() like I
mentioned on the bug, since that ought to be more stable?

[danakj, 2016/06/29 19:47:39]

SurfaceSize() is passed from LTHI to Renderer::DrawFrame, which does Resize() on
the OutputSurface, which will return it from SurfaceSize() thereafter. The
external viewport size seems to be the input value to me, and SurfaceSize would
be from the same source, but be from the previous frame.

+  gfx::Rect ViewportRectForTilePriority() const;
   std::unique_ptr<ScrollbarAnimationController>
   CreateScrollbarAnimationController(int scroll_layer_id);
   void DidAnimateScrollOffset();