Move .ico hashing to icon_util

ui/gfx/icon_util.h

Index: ui/gfx/icon_util.h
diff --git a/ui/gfx/icon_util.h b/ui/gfx/icon_util.h
index 7ce5606f525d0f7b92b6ceaef7158ca0e1dec360..61174bbf91c80bd24f4fe5d2fec3301e18bd7d43 100644
--- a/ui/gfx/icon_util.h
+++ b/ui/gfx/icon_util.h
@@ -18,6 +18,7 @@
 
 namespace base {
 class FilePath;
+struct MD5Digest;
 }
 
 namespace gfx {
@@ -136,6 +137,19 @@ class UI_EXPORT IconUtil {
                                    const void* dib_bits,
                                    size_t dib_size);
 
+  // Calculates checksum of an icon family using MD5.
+  // The checksum is derived from all of the icons in the family.
+  static void GetImageCheckSum(const gfx::ImageFamily& image,
+                               base::MD5Digest* digest);

[Alexei Svitkine (slow), 2013/05/09 15:34:57]

Can this be private to the implementation, in an anonymous namespace?

Or is there a use case for other code using? (In which case, perhaps it
shouldn't be in this file but in a more general gfx util location.)

However, I'd say unless some other code will soon use this from the outside,
move it to the impl.

+
+  // Saves |image| as an |icon_file| with the checksum.

[Alexei Svitkine (slow), 2013/05/09 15:34:57]

Please expand the comment to mention how this actually works.

+  static bool SaveIconWithCheckSum(const base::FilePath& icon_file,
+                                   const gfx::ImageFamily& image);
+
+  // Returns true if |icon_file| is missing or different from |image|.
+  static bool ShouldUpdateIcon(const base::FilePath& icon_file,

[Alexei Svitkine (slow), 2013/05/09 15:34:57]

Could you write a simple unit test for this?

+                               const gfx::ImageFamily& image);
+
  private:
   // The icon format is published in the MSDN but there is no definition of
   // the icon file structures in any of the Windows header files so we need to