ui: Export a function that's used by a test.

BUG=90078
TEST=none
TBR=sky

Review URL: http://codereview.chromium.org/9699080

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@126969 0039d316-1c4b-4281-b951-d872f2087c98

ui/gfx/mac/nsimage_cache.h

-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -28,7 +28,7 @@ namespace gfx {
 UI_EXPORT NSImage* GetCachedImageWithName(NSString* name);
 
 // Clears the image cache.
-void ClearCachedImages(void);
+UI_EXPORT void ClearCachedImages(void);
 
 }  // namespace gfx