Set device scale factor in CompositorFrame and scale frame size in WS.

services/ui/surfaces/display_compositor.cc

Index: services/ui/surfaces/display_compositor.cc
diff --git a/services/ui/surfaces/display_compositor.cc b/services/ui/surfaces/display_compositor.cc
index ffa022361709f1b6c81c83281b93532cbf8dbe79..bce51bcbea5e8751d736115d7648a7999d5a1566 100644
--- a/services/ui/surfaces/display_compositor.cc
+++ b/services/ui/surfaces/display_compositor.cc
@@ -226,6 +226,7 @@ void DisplayCompositor::OnSurfaceCreated(const cc::SurfaceId& surface_id,
                                          const gfx::Size& frame_size,
                                          float device_scale_factor) {
   DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(device_scale_factor);

[kylechar, 2016/12/15 18:25:03]

DCHECK_GT(device_scale_factor, 0.0f) maybe so it's clear it's a float?

[riajiang, 2016/12/15 19:01:43]

Done.

   // We can get into a situation where multiple CompositorFrames arrive for a
   // CompositorFrameSink before the DisplayCompositorClient can add any
   // references for the frame. When the second frame with a new size arrives,