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
+      UMA_HISTOGRAM_EXACT_LINEAR("Media.UncacheableReason", shift,

[rkaplow, 2017/03/29 18:02:51]

not sure why this can't be an enum either. Add a TODO to fix?

[dcheng, 2017/03/29 18:24:41]

I think it's because the enum itself is a bitmask style enum, so we'd have to
define two separate enums to make this work out nicely. Do you still want a
TODO?

[rkaplow, 2017/03/29 23:21:17]

Well, the team can evaluate if they want to change. LINEAR is intended for
capturing numeric data with linear sized buckets. It may be worth to have the
bitmask map to an underlying enum and they can use that.

If we want to keep it like this I'd at least have a comment explaining why we're
faking an enum with a linear macro

[dcheng, 2017/03/30 00:41:59]

Done.

+                                 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