Explicitly specify contents scale for SurfaceLayer.

cc/layers/surface_layer.cc

Index: cc/layers/surface_layer.cc
diff --git a/cc/layers/surface_layer.cc b/cc/layers/surface_layer.cc
index ee376aad4e025679bd5a137d44678edbe1180c27..ab6289ef4265d1b5a85ac275986fca0515a515bb 100644
--- a/cc/layers/surface_layer.cc
+++ b/cc/layers/surface_layer.cc
@@ -44,6 +44,7 @@ scoped_refptr<SurfaceLayer> SurfaceLayer::Create(
 SurfaceLayer::SurfaceLayer(const SatisfyCallback& satisfy_callback,
                            const RequireCallback& require_callback)
     : Layer(),
+      surface_scale_(1.f),
       satisfy_callback_(satisfy_callback),
       require_callback_(require_callback) {
 }
@@ -53,10 +54,13 @@ SurfaceLayer::~SurfaceLayer() {
   DCHECK(destroy_sequence_.is_null());
 }
 
-void SurfaceLayer::SetSurfaceId(SurfaceId surface_id, const gfx::Size& size) {
+void SurfaceLayer::SetSurfaceId(SurfaceId surface_id,
+                                float scale,
+                                const gfx::Size& size) {
   SatisfyDestroySequence();
   surface_id_ = surface_id;
   surface_size_ = size;
+  surface_scale_ = scale;
   CreateNewDestroySequence();
 
   UpdateDrawsContent(HasDrawableContent());
@@ -94,12 +98,8 @@ void SurfaceLayer::CalculateContentsScale(float ideal_contents_scale,
                                           float* contents_scale_y,
                                           gfx::Size* content_bounds) {
   *content_bounds = surface_size_;
-  *contents_scale_x =
-      bounds().IsEmpty() ? 1.f : static_cast<float>(content_bounds->width()) /
-                                     bounds().width();
-  *contents_scale_y =
-      bounds().IsEmpty() ? 1.f : static_cast<float>(content_bounds->height()) /
-                                     bounds().height();
+  *contents_scale_x = surface_scale_;
+  *contents_scale_y = surface_scale_;
 }
 
 void SurfaceLayer::CreateNewDestroySequence() {