Make tile size a function of the device scale factor.

cc/trees/layer_tree_impl.h

 // Copyright 2012 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.
 
 #ifndef CC_TREES_LAYER_TREE_IMPL_H_
 #define CC_TREES_LAYER_TREE_IMPL_H_
 
 #include <map>
 #include <set>
 #include <string>
@@ skipping 87 matching lines @@
   bool IsPendingTree() const;
   bool IsRecycleTree() const;
   bool IsSyncTree() const;
   LayerImpl* FindActiveTreeLayerById(int id);
   LayerImpl* FindPendingTreeLayerById(int id);
   bool PinchGestureActive() const;
   BeginFrameArgs CurrentBeginFrameArgs() const;
   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();
   bool use_gpu_rasterization() const;
   GpuRasterizationStatus GetGpuRasterizationStatus() const;
   bool create_low_res_tiling() const;
   bool RequiresHighResToDraw() const;
   bool SmoothnessTakesPriority() const;
   VideoFrameControllerClient* GetVideoFrameControllerClient() const;
   AnimationHost* animation_host() const {
@@ skipping 466 matching lines @@
 
   std::unique_ptr<PendingPageScaleAnimation> pending_page_scale_animation_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_IMPL_H_