DisplayCompositor should enforce invariant that frame size and device scale factor are fixed

cc/surfaces/surface.h

Index: cc/surfaces/surface.h
diff --git a/cc/surfaces/surface.h b/cc/surfaces/surface.h
index f35740ab3f0ea3ae2b1141129ca50c74b8136075..792fa56e585db642ee6139b5cf77766f18bd65b3 100644
--- a/cc/surfaces/surface.h
+++ b/cc/surfaces/surface.h
@@ -23,6 +23,7 @@
 #include "cc/surfaces/pending_frame_observer.h"
 #include "cc/surfaces/surface_factory.h"
 #include "cc/surfaces/surface_id.h"
+#include "cc/surfaces/surface_info.h"
 #include "cc/surfaces/surface_sequence.h"
 #include "cc/surfaces/surfaces_export.h"
 #include "ui/gfx/geometry/size.h"
@@ -121,6 +122,8 @@ class CC_SURFACES_EXPORT Surface {
   bool destroyed() const { return destroyed_; }
   void set_destroyed(bool destroyed) { destroyed_ = destroyed; }
 
+  const SurfaceInfo& surface_info() { return surface_info_.value(); }
+
  private:
   void ActivatePendingFrame();
   // Called when all of the surface's dependencies have been resolved.
@@ -157,6 +160,8 @@ class CC_SURFACES_EXPORT Surface {
 
   DrawCallback draw_callback_;
 
+  base::Optional<SurfaceInfo> surface_info_;

[Fady Samuel, 2017/03/17 19:57:44]

I wouldn't make this optional. I would instead take this in the constructor?

+
   DISALLOW_COPY_AND_ASSIGN(Surface);
 };