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

components/favicon/core/large_icon_service.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/favicon/core/large_icon_service.h"
 
 #include <memory>
 
 #include "base/bind.h"
 #include "base/location.h"
@@ skipping 99 matching lines @@
         *bitmap = image.AsBitmap();
       }
       return;
     }
   }
 
   if (!fallback_icon_style)
     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);
+    // The size must be positive, we cap to 128 to avoid the sparse histogram
+    // to explode (having too many different values, server-side). Size 128
+    // already indicates that there is a problem in the code, 128 px _should_ be
+    // enough in all current UI surfaces.
+    fallback_icon_size = db_result.pixel_size.width();
+    DCHECK_GT(fallback_icon_size, 0);
+    fallback_icon_size = std::min(fallback_icon_size, 128);
   }
+  UMA_HISTOGRAM_SPARSE_SLOWLY("Favicons.LargeIconService.FallbackSize",
+                              fallback_icon_size);
 }
 
 // Processes the bitmap data returned from the FaviconService as part of a
 // LargeIconService request.
 class LargeIconWorker : public base::RefCountedThreadSafe<LargeIconWorker> {
  public:
   // Exactly one of the callbacks is expected to be non-null.
   LargeIconWorker(int min_source_size_in_pixel,
                   int desired_size_in_pixel,
                   favicon_base::LargeIconCallback raw_bitmap_callback,
@@ skipping 210 matching lines @@
   // TODO(beaudoin): For now this is just a wrapper around
   //   GetLargestRawFaviconForPageURL. Add the logic required to select the best
   //   possible large icon. Also add logic to fetch-on-demand when the URL of
   //   a large icon is known but its bitmap is not available.
   return favicon_service_->GetLargestRawFaviconForPageURL(
       page_url, large_icon_types_, min_source_size_in_pixel,
       base::Bind(&LargeIconWorker::OnIconLookupComplete, worker), tracker);
 }
 
 }  // namespace favicon