Add hints for potential overlay promotion on android.

cc/output/overlay_candidate_validator.h

Index: cc/output/overlay_candidate_validator.h
diff --git a/cc/output/overlay_candidate_validator.h b/cc/output/overlay_candidate_validator.h
index 09d380b82a9227b13bd343f91c3234ce00dc74bf..cd47e74038bc45f7309b1a5f6f0f601cae0e6b89 100644
--- a/cc/output/overlay_candidate_validator.h
+++ b/cc/output/overlay_candidate_validator.h
@@ -8,6 +8,7 @@
 #include <vector>
 
 #include "cc/base/cc_export.h"
+#include "cc/base/resource_id.h"
 #include "cc/output/overlay_candidate.h"
 #include "cc/output/overlay_processor.h"
 
@@ -31,6 +32,13 @@ class CC_EXPORT OverlayCandidateValidator {
   // coordinates if necessary.
   virtual void CheckOverlaySupport(OverlayCandidateList* surfaces) = 0;
 
+  // Called before beginning a new pass for overlay promotion to clear out any
+  // promotable resources.  One must CheckoverlaySupport() again.
+  virtual void ClearPromotableResources() {}
+
+  // Returns whether |resource_id| is promotable.
+  virtual bool IsResourcePromotable(ResourceId resource_id);

[piman, 2016/11/23 00:37:25]

Super nit: in the context of OverlayCandidateValidator, IsResourcePromotable
suggests "this resource can be put in an overlay" as in "right now", whereas I
think you mean "this resource would be ok to put in an overlay, but only if it's
switched to SurfaceView, but it isn't right now". Not sure what is the best name
to convey the concept...

[liberato (no reviews please), 2016/12/01 20:59:11]

i've since moved the set into OverlayCandidateList, since it was a little weird
to have this statefulness here.

named the set 'promotable_resource_hints_'

+
   virtual ~OverlayCandidateValidator() {}
 };