Modifies GetPlatformImageColor() to check the color of a given point.

ui/gfx/image/image_unittest_util_mac.mm

 // 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.
 
 #import <AppKit/AppKit.h>
 
 #include "skia/ext/skia_utils_mac.h"
 #include "ui/gfx/image/image_unittest_util.h"
 
 namespace gfx {
 namespace test {
 
-SkColor GetPlatformImageColor(PlatformImage image) {
+  SkColor GetPlatformImageColor(PlatformImage image, int x, int y) {
   [image lockFocus];
-  NSColor* color = NSReadPixel(NSMakePoint(10, 10));
+  NSColor* color = NSReadPixel(NSMakePoint(x, y));
   [image unlockFocus];
   return NSDeviceColorToSkColor(color);
 }
 
 }  // namespace test
 }  // namespace gfx