Fix assert in GetOverlayRect when transforming video with Ozone overlay

cc/output/overlay_candidate_validator.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_OUTPUT_OVERLAY_CANDIDATE_VALIDATOR_H_
 #define CC_OUTPUT_OVERLAY_CANDIDATE_VALIDATOR_H_
 
 #include <vector>
 
 #include "cc/base/cc_export.h"
 #include "cc/output/overlay_candidate.h"
 
 namespace cc {
 
 // This class that can be used to answer questions about possible overlay
 // configurations for a particular output device.
 class CC_EXPORT OverlayCandidateValidator {
  public:
   // 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
-  // to be traditionally composited.
+  // to be traditionally composited. Candidates with |overlay_handled| set to
+  // true must also have their |display_rect| converted to integer
+  // coordinates if necessary.
   virtual void CheckOverlaySupport(OverlayCandidateList* surfaces) = 0;
 
   virtual ~OverlayCandidateValidator() {}
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_OVERLAY_CANDIDATE_VALIDATOR_H_