Add DCLayerOverlayProcessor and supporting DCLayer structures.

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..5c6ccf5d056e7b1738bc2e728867191bc4fef455 100644
--- a/cc/output/overlay_candidate_validator.h
+++ b/cc/output/overlay_candidate_validator.h
@@ -23,6 +23,10 @@ class CC_EXPORT OverlayCandidateValidator {
   // Returns true if draw quads can be represented as CALayers (Mac only).
   virtual bool AllowCALayerOverlays() = 0;
 
+  // Returns true if draw quads can be represented as Direct Composition
+  // Visuals (Windows only).
+  virtual bool AllowDCLayerOverlays() = 0;
+
   // A list of possible overlay candidates is presented to this function.
   // The expected result is that those candidates that can be in a separate
   // plane are marked with |overlay_handled| set to true, otherwise they are