cc: Do GatherPixelRefs from skia at record time

cc/base/util.h

 // Copyright 2012 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_BASE_UTIL_H_
 #define CC_BASE_UTIL_H_
 
 namespace cc {
 
 template <typename T> T RoundUp(T n, T mul) {
-  return ((n + mul - 1) / mul) * mul;
+  return (n > 0) ? ((n + mul - 1) / mul) * mul
+                 : (n / mul) * mul;
+}
+
+template <typename T> T RoundDown(T n, T mul) {
+  return (n > 0) ? (n / mul) * mul
+                 : ((n - mul + 1) / mul) * mul;
 }
 
 }  // namespace cc
 
 #endif  // CC_BASE_UTIL_H_