Make UMA_HISTOGRAM_ENUMERATION work with scoped enums.

media/blink/resource_multibuffer_data_provider.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 "media/blink/resource_multibuffer_data_provider.h"
 
 #include <stddef.h>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 245 matching lines @@
                                         GetCacheValidUntil(response));
 
   uint32_t reasons = GetReasonsForUncacheability(response);
   destination_url_data->set_cacheable(reasons == 0);
   UMA_HISTOGRAM_BOOLEAN("Media.CacheUseful", reasons == 0);
   int shift = 0;
   int max_enum = base::bits::Log2Ceiling(kMaxReason);
   while (reasons) {
     DCHECK_LT(shift, max_enum);  // Sanity check.
     if (reasons & 0x1) {
-      UMA_HISTOGRAM_ENUMERATION("Media.UncacheableReason", shift,
-                                max_enum);  // PRESUBMIT_IGNORE_UMA_MAX
+      // Note: this uses an exact linear UMA to fake an enum UMA, as the actual
+      // enum is a bitmask.
+      UMA_HISTOGRAM_EXACT_LINEAR("Media.UncacheableReason", shift,
+                                 max_enum);  // PRESUBMIT_IGNORE_UMA_MAX
     }
 
     reasons >>= 1;
     ++shift;
   }
 
   // Expected content length can be |kPositionNotSpecified|, in that case
   // |content_length_| is not specified and this is a streaming response.
   int64_t content_length = response.expectedContentLength();
   bool end_of_file = false;
@@ skipping 269 matching lines @@
   }
 
   if (byte_pos() != first_byte_position) {
     return false;
   }
 
   return true;
 }
 
 }  // namespace media