ui: Add a minor unittest to check to work correctly with a empty clip in Blit.ScrollCanvas

ui/gfx/blit_unittest.cc

 // Copyright (c) 2010 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.
 
 #include "base/basictypes.h"
 #include "base/memory/shared_memory.h"
 #include "skia/ext/platform_canvas.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gfx/blit.h"
 #include "ui/gfx/point.h"
@@ skipping 62 matching lines @@
 
   // Sanity check on input.
   VerifyCanvasValues<5, 5>(canvas.get(), initial_values);
 
   // Scroll none and make sure it's a NOP.
   gfx::ScrollCanvas(canvas.get(),
                     gfx::Rect(0, 0, kCanvasWidth, kCanvasHeight),
                     gfx::Vector2d(0, 0));
   VerifyCanvasValues<5, 5>(canvas.get(), initial_values);
 
+  // Scroll with a empty clip and make sure it's a NOP.
+  gfx::Rect empty_clip(1, 1, 0, 0);
+  gfx::ScrollCanvas(canvas.get(), empty_clip, gfx::Vector2d(0, 1));
+  VerifyCanvasValues<5, 5>(canvas.get(), initial_values);
+
   // Scroll the center 3 pixels up one.
   gfx::Rect center_three(1, 1, 3, 3);
   gfx::ScrollCanvas(canvas.get(), center_three, gfx::Vector2d(0, -1));
   uint8 scroll_up_expected[kCanvasHeight][kCanvasWidth] = {
       { 0x00, 0x01, 0x02, 0x03, 0x04 },
       { 0x10, 0x21, 0x22, 0x23, 0x14 },
       { 0x20, 0x31, 0x32, 0x33, 0x24 },
       { 0x30, 0x31, 0x32, 0x33, 0x34 },
       { 0x40, 0x41, 0x42, 0x43, 0x44 }};
   VerifyCanvasValues<5, 5>(canvas.get(), scroll_up_expected);
@@ skipping 64 matching lines @@
       { 0x30, 0x31, 0x32, 0x33, 0x34 },
       { 0x40, 0x41, 0x42, 0x43, 0x44 }};
   SetToCanvas<5, 5>(canvas.get(), initial_values);
 
   // Sanity check on input.
   VerifyCanvasValues<5, 5>(canvas.get(), initial_values);
 }
 
 #endif