Implement transform snapping for gfx::Transforms.

ui/gfx/transform_util.h

Index: ui/gfx/transform_util.h
diff --git a/ui/gfx/transform_util.h b/ui/gfx/transform_util.h
index 07bf0d5703ebb6e0768e0510566201a052bd27a2..09701547a6042cd808b5766dccd016df84e8364f 100644
--- a/ui/gfx/transform_util.h
+++ b/ui/gfx/transform_util.h
@@ -11,6 +11,7 @@
 namespace gfx {
 
 class Point;
+class Rect;
 
 // Returns a scale transform at |anchor| point.
 GFX_EXPORT Transform GetScaleTransform(const Point& anchor, float scale);
@@ -53,6 +54,10 @@ GFX_EXPORT bool DecomposeTransform(DecomposedTransform* out,
 // http://www.w3.org/TR/css3-3d-transforms/.
 GFX_EXPORT Transform ComposeTransform(const DecomposedTransform& decomp);
 
+GFX_EXPORT bool SnapRotation(Transform* out,
+                             const Transform& transform,
+                             const Rect& viewport);
+
 }  // namespace gfx
 
 #endif  // UI_GFX_TRANSFORM_UTIL_H_