ui: Prefer +/- operators to apply offsets.

ui/gfx/blit.h

 // Copyright (c) 2011 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_BLIT_H_
 #define UI_GFX_BLIT_H_
 
 #include "ui/gfx/native_widget_types.h"
 #include "ui/base/ui_export.h"
 
@@ skipping 22 matching lines @@
                                    const Rect& dst_rect,
                                    SkCanvas *src_canvas,
                                    const Point& src_origin);
 
 // Blits a rectangle from the source canvas into the destination canvas.
 UI_EXPORT void BlitCanvasToCanvas(SkCanvas *dst_canvas,
                                   const Rect& dst_rect,
                                   SkCanvas *src_canvas,
                                   const Point& src_origin);
 
-// Scrolls the given subset of the given canvas by the given amount.
+// Scrolls the given subset of the given canvas by the given offset.
 // The canvas should not have a clip or a transform applied, since platforms
 // may implement those operations differently.
 UI_EXPORT void ScrollCanvas(SkCanvas* canvas,
                             const Rect& clip,
-                            const Vector2d& amount);
+                            const Vector2d& offset);
 
 }  // namespace gfx
 
 #endif  // UI_GFX_BLIT_H_