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 be5ba4c03ce6c46ecf99f8b4b7515494f2150f26..40733e3f401da1744400413b9a35fb96b263588c 100644
--- a/ui/gfx/transform_util.h
+++ b/ui/gfx/transform_util.h
@@ -11,6 +11,7 @@
 namespace gfx {
 
 class Point;
+class RectF;
 
 // Returns a scale transform at |anchor| point.
 UI_EXPORT Transform GetScaleTransform(const Point& anchor, float scale);
@@ -51,6 +52,11 @@ UI_EXPORT bool DecomposeTransform(DecomposedTransform* out,
 // http://www.w3.org/TR/css3-3d-transforms/.
 UI_EXPORT Transform ComposeTransform(const DecomposedTransform& decomp);
 
+UI_EXPORT bool SnapRotation(DecomposedTransform* out,
+                            const DecomposedTransform& decomp,
+                            const Transform& transform,
+                            const RectF& viewport);
+
 }  // namespace gfx
 
 #endif  // UI_GFX_TRANSFORM_UTIL_H_