[LargeIconService] Report size of favicon for fallback style to UMA

components/favicon/core/large_icon_service.cc

Index: components/favicon/core/large_icon_service.cc
diff --git a/components/favicon/core/large_icon_service.cc b/components/favicon/core/large_icon_service.cc
index c202c244ff784f4bb1634ee2b80da8a9e69e19b7..ea0750178bc8f9062f6376c4d7a5d74c3b3c64e5 100644
--- a/components/favicon/core/large_icon_service.cc
+++ b/components/favicon/core/large_icon_service.cc
@@ -117,10 +117,15 @@ void ProcessIconOnBackgroundThread(
     return;
 
   *fallback_icon_style = favicon_base::FallbackIconStyle();
+  int fallback_icon_size = 0;
   if (db_result.is_valid()) {
     favicon_base::SetDominantColorAsBackground(db_result.bitmap_data,
                                                fallback_icon_style);
+    fallback_icon_size = db_result.pixel_size.width();
+    DCHECK_GT(fallback_icon_size, 0);

[Ilya Sherman, 2017/04/13 07:46:29]

Hmm, if the API allows setting an arbitrary upper bound, then what guarantees
that the histogram will not explode?

   }
+  UMA_HISTOGRAM_SPARSE_SLOWLY("Favicons.LargeIconService.FallbackSize",
+                              fallback_icon_size);
 }
 
 // Processes the bitmap data returned from the FaviconService as part of a