Give SelectFaviconFrames a quality score.

chrome/browser/favicon/select_favicon_frames.h

Index: chrome/browser/favicon/select_favicon_frames.h
diff --git a/chrome/browser/favicon/select_favicon_frames.h b/chrome/browser/favicon/select_favicon_frames.h
index 07493c93e0d145fae2161cff3c570ab27f1603df..768d394653caa5568c998be716f09be145824932 100644
--- a/chrome/browser/favicon/select_favicon_frames.h
+++ b/chrome/browser/favicon/select_favicon_frames.h
@@ -19,9 +19,15 @@ class ImageSkia;
 // ImageSkia that's desired_size x desired_size pixels big. This
 // function adds a representation at every desired scale factor.
 // If desired_size is 0, the largest bitmap is returned unmodified.
+// If score is non-NULL, it receive a score between 0 (bad) and 1 (good)
+// that describes how well |bitmaps| were able to produce an image at
+// |desired_size| for |scale_factors|.
+// The score is arbitrary, but it's best for exact size matches,
+// and gets worse the more resampling needs to happen.
 gfx::ImageSkia SelectFaviconFrames(
     const std::vector<SkBitmap>& bitmaps,
     const std::vector<ui::ScaleFactor>& scale_factors,
-    int desired_size);
+    int desired_size,
+    float* score);
 
 #endif  // CHROME_BROWSER_FAVICON_SELECT_FAVICON_FRAMES_H_