Change return type of FaviconTabHelper::GetFavicon() to gfx::Image.

ui/gfx/image/image.cc

Index: ui/gfx/image/image.cc
diff --git a/ui/gfx/image/image.cc b/ui/gfx/image/image.cc
index ea302ab58a6297a3a9a9861d93be30ab5c29698a..9854787733b7cf9029de07fec2ffb50081d147b3 100644
--- a/ui/gfx/image/image.cc
+++ b/ui/gfx/image/image.cc
@@ -337,6 +337,14 @@ NSImage* Image::ToNSImage() const {
 }
 #endif
 
+SkBitmap Image::AsBitmap() const {
+  return IsEmpty() ? SkBitmap() : *ToSkBitmap();
+}
+
+ImageSkia Image::AsImageSkia() const {
+  return IsEmpty() ? ImageSkia(SkBitmap()) : *ToImageSkia();
+}
+
 ImageSkia* Image::CopyImageSkia() const {
   return new ImageSkia(*ToImageSkia());
 }