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 b6da7b0782d3b63d461fa685912bff11b0c8cfda..7e43a0ed2b0eedcd1f144e935d3e35745f31bcaa 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 +52,10 @@ 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& in,
+                            const RectF& viewport);
+
 }  // namespace gfx
 
 #endif  // UI_GFX_TRANSFORM_UTIL_H_