cc: Do GatherPixelRefs from skia at record time

cc/base/util.h

Index: cc/base/util.h
diff --git a/cc/base/util.h b/cc/base/util.h
index b5a58c76b3b1199a4b9ebc0ce0bacc5a5dc78e36..2bf2723d4bea2c1eab42d46a439f6e8af3d98996 100644
--- a/cc/base/util.h
+++ b/cc/base/util.h
@@ -8,7 +8,13 @@
 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