Implement transform snapping for gfx::Transforms.

ui/gfx/transform_util.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_GFX_TRANSFORM_UTIL_H_
 #define UI_GFX_TRANSFORM_UTIL_H_
 
 #include "ui/gfx/gfx_export.h"
 #include "ui/gfx/transform.h"
 
 namespace gfx {
 
 class Point;
+class RectF;
 
 // Returns a scale transform at |anchor| point.
 UI_EXPORT Transform GetScaleTransform(const Point& anchor, float scale);
 
 // Contains the components of a factored transform. These components may be
 // blended and recomposed.
 struct UI_EXPORT DecomposedTransform {
   // The default constructor initializes the components in such a way that
   // if used with Compose below, will produce the identity transform.
   DecomposedTransform();
@@ skipping 20 matching lines @@
 // and rotation components following the routines detailed in this spec:
 // http://www.w3.org/TR/css3-3d-transforms/.
 UI_EXPORT bool DecomposeTransform(DecomposedTransform* out,
                                   const Transform& transform);
 
 // Composes a transform from the given translation, scale, skew, prespective,
 // and rotation components following the routines detailed in this spec:
 // 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_