Never decode the favicon in FaviconUtil::SelectFaviconFramesFromPNGs() to...

Never decode the favicon in FaviconUtil::SelectFaviconFramesFromPNGs() to SkBitmap when the desired size is 0. The decoding is unnecessary.
Giving the largest PNG a scale factor of 100P matches the behavior in SelectFaviconFrames().
This is a corner case that I need to fix in order fix 278457

BUG=278457
TEST=None

Review URL: https://chromiumcodereview.appspot.com/23569008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@222070 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/favicon/favicon_util.cc

@@ -32,7 +32,7 @@ std::vector<gfx::ImagePNGRep> SelectFaviconFramesFromPNGsWithoutResizing(
     return png_reps;
 
   // A |favicon_size| of 0 indicates that the largest frame is desired.
-  if (favicon_size == 0 && scale_factors.size() == 1) {
+  if (favicon_size == 0) {
     int maximum_area = 0;
     scoped_refptr<base::RefCountedMemory> best_candidate;
     for (size_t i = 0; i < png_data.size(); ++i) {
@@ -43,7 +43,7 @@ std::vector<gfx::ImagePNGRep> SelectFaviconFramesFromPNGsWithoutResizing(
       }
     }
     png_reps.push_back(gfx::ImagePNGRep(best_candidate,
-                                        scale_factors[0]));
+                                        ui::SCALE_FACTOR_100P));
     return png_reps;
   }
 
@@ -134,6 +134,11 @@ gfx::Image FaviconUtil::SelectFaviconFramesFromPNGs(
       SelectFaviconFramesFromPNGsWithoutResizing(png_data, scale_factors,
           favicon_size);
 
+  // SelectFaviconFramesFromPNGsWithoutResizing() should have selected the
+  // largest favicon if |favicon_size| == 0.
+  if (favicon_size == 0)
+    return gfx::Image(png_reps);
+
   std::vector<ui::ScaleFactor> scale_factors_to_generate = scale_factors;
   for (size_t i = 0; i < png_reps.size(); ++i) {
     std::vector<ui::ScaleFactor>::iterator it = std::find(