Align physical pixels of scrolled layers

cc/math_util.h

Index: cc/math_util.h
diff --git a/cc/math_util.h b/cc/math_util.h
index 8c1ca88675dbde5e7aee2e77ab6ad0d1684beee0..24a155d74422c31ea8a3cd8f1a7c54bfc8e85e88 100644
--- a/cc/math_util.h
+++ b/cc/math_util.h
@@ -5,6 +5,8 @@
 #ifndef CC_MATH_UTIL_H_
 #define CC_MATH_UTIL_H_
 
+#include <cmath>
+
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "cc/cc_export.h"
@@ -81,6 +83,9 @@ public:
     static float Deg2Rad(float deg)  { return deg * PI_FLOAT / 180; }
     static float Rad2Deg(float rad)  { return rad * 180 / PI_FLOAT; }
 
+    static float Round(float f)  { return (f > 0.f) ? std::floor(f + 0.5f) : std::ceil(f - 0.5f); }
+    static double Round(double d)  { return (d > 0.0) ? std::floor(d + 0.5) : std::ceil(d - 0.5); }
+
     // Background: Existing transform code does not do the right thing in
     // mapRect / mapQuad / projectQuad when there is a perspective projection that causes
     // one of the transformed vertices to go to w < 0. In those cases, it is necessary to