Fall back to the default favicon on invalid favicon files.

ui/gfx/image/image.h

Index: ui/gfx/image/image.h
diff --git a/ui/gfx/image/image.h b/ui/gfx/image/image.h
index 04a79daffec0673be643d72e04bf7a53e760f501..b643362fcf06376c34705ca94b12f1593feb9c6f 100644
--- a/ui/gfx/image/image.h
+++ b/ui/gfx/image/image.h
@@ -97,7 +97,7 @@ class UI_EXPORT Image {
 
   // Converts the Image to the desired representation and stores it internally.
   // The returned result is a weak pointer owned by and scoped to the life of
-  // the Image.
+  // the Image. Must only be called if IsEmpty() is false.
   const SkBitmap* ToSkBitmap() const;
   const ImageSkia* ToImageSkia() const;
 #if defined(TOOLKIT_GTK)
@@ -110,10 +110,15 @@ class UI_EXPORT Image {
   // Same as ToSkBitmap(), but returns a null SkBitmap if this image is empty.
   SkBitmap AsBitmap() const;
 
-  // Same as ToSkBitmap(), but returns a ImageSkia with a null SkBitmap if this
+  // Same as ToImageSkia(), but returns an empty ImageSkia if this
   // image is empty.
   ImageSkia AsImageSkia() const;
 
+#if defined(OS_MACOSX)
+  // Same as ToSkBitmap(), but returns nil if this image is empty.
+  NSImage* AsNSImage() const;
+#endif
+
   // Performs a conversion, like above, but returns a copy of the result rather
   // than a weak pointer. The caller is responsible for deleting the result.
   // Note that the result is only a copy in terms of memory management; the