Allow UmaHistogramEnumeration to be used with enum classes.

base/metrics/histogram_functions.h

 // Copyright 2016 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.
 
 #ifndef BASE_METRICS_HISTOGRAM_FUNCTIONS_H_
 #define BASE_METRICS_HISTOGRAM_FUNCTIONS_H_
 
 #include "base/metrics/histogram.h"
 #include "base/metrics/histogram_base.h"
 #include "base/time/time.h"
@@ skipping 25 matching lines @@
 
 // For adding sample to enum histogram.
 // Sample usage:
 //   base::UmaHistogramEnumeration("My.Enumeration", VALUE, EVENT_MAX_VALUE);
 // Note that new Enum values can be added, but existing enums must never be
 // renumbered or deleted and reused.
 template <typename T>
 void UmaHistogramEnumeration(const std::string& name, T sample, T max) {
   static_assert(std::is_enum<T>::value,
                 "Non enum passed to UmaHistogramEnumeration");
-  return UmaHistogramExactLinear(name, static_cast<int>(sample), max);
+  DCHECK_GE(static_cast<int64_t>(max), 0);
+  DCHECK_LE(static_cast<int64_t>(max), INT_MAX);
+  DCHECK_GE(static_cast<int64_t>(sample), 0);
+  DCHECK_LE(sample, max);

[benwells, 2017/04/06 07:30:01]

How is this? Some questions:
- do you have a better way to do this? I tried doing things with static_assert
but couldn't make it actually work. 
- I am pretty sure there aren't problems with this with numbers between
INT64_MAX and UINT64_MAX, but tell me if I'm wrong.
- Is it OK to do this in an inline function?

[benwells, 2017/04/06 07:40:24]

A smart person here suggested this:
DCHECK_EQ(max, static_cast<T>(static_cast<int>(max)))

WDYT?

[dcheng, 2017/04/06 07:47:05]

Yeah, static assert won't work here.
I think this is fine. I think the number of DCHECKs could probably be reduced
though.
DCHECK_LE(static_cast<uintmax_t>(max), static_cast<uintmax_t>(INT_MAX));
DCHECK_LE(static_cast<uintmax_t>(sample), static_cast<uintmax_t>(max));

which would cover the same thing (though it's slightly more subtle)
Yeah, it's a DCHECK so it shouldn't* affect official builds.

* of course it does sometimes. But we fixed all the ones that we can, and things
like this hopefully aren't affected.

[benwells, 2017/04/06 08:16:48]

OK ... yeah, subtle :) Thanks!

+  return UmaHistogramExactLinear(name, static_cast<int>(sample),
+                                 static_cast<int>(max));
 }
 
 // For adding boolean sample to histogram.
 // Sample usage:
 //   base::UmaHistogramBoolean("My.Boolean", true)
 BASE_EXPORT void UmaHistogramBoolean(const std::string& name, bool sample);
 
 // For adding histogram with percent.
 // Percents are integer between 1 and 100.
 // Sample usage:
@@ skipping 34 matching lines @@
 
 // For recording memory related histograms.
 // Used to measure common KB-granularity memory stats. Range is up to 500M.
 BASE_EXPORT void UmaHistogramMemoryKB(const std::string& name, int sample);
 // Used to measure common MB-granularity memory stats. Range is up to ~64G.
 BASE_EXPORT void UmaHistogramMemoryLargeMB(const std::string& name, int sample);
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_FUNCTIONS_H_