Add support for PNG representation in gfx::Image

ui/gfx/image/image_unittest_util.cc

Index: ui/gfx/image/image_unittest_util.cc
diff --git a/ui/gfx/image/image_unittest_util.cc b/ui/gfx/image/image_unittest_util.cc
index 04620a7f66c3677241226809a7b811ca8b6066b5..e28e7828defe7678ff98879f579dae5369821404 100644
--- a/ui/gfx/image/image_unittest_util.cc
+++ b/ui/gfx/image/image_unittest_util.cc
@@ -113,6 +113,16 @@ PlatformImage ToPlatformType(const gfx::Image& image) {
 #endif
 }
 
+PlatformImage CopyPlatformType(const gfx::Image& image) {
+#if defined(OS_MACOSX)
+  return image.CopyNSImage();
+#elif defined(TOOLKIT_GTK)
+  return image.CopyGdkPixbuf();
+#else
+  return *image.ToSkBitmap();
+#endif
+}
+
 bool IsPlatformImageValid(PlatformImage image) {
 #if defined(OS_MACOSX) || defined(TOOLKIT_GTK)
   return image != NULL;