Move STATIC_HISTOGRAM_POINTER_GROUP into histogram_macros.h.

base/metrics/histogram_macros.h

 // Copyright 2014 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_MACROS_H_
 #define BASE_METRICS_HISTOGRAM_MACROS_H_
 
 #include "base/metrics/histogram.h"
 #include "base/metrics/histogram_macros_internal.h"
 #include "base/metrics/histogram_macros_local.h"
@@ skipping 238 matching lines @@
 // infrequently recorded values since the implementation is slower
 // and takes more memory.
 //
 // For instance, Sqlite.Version.* are sparse because for any given database,
 // there's going to be exactly one version logged.
 // The |sample| can be a negative or non-negative number.
 #define UMA_HISTOGRAM_SPARSE_SLOWLY(name, sample)                              \
     INTERNAL_HISTOGRAM_SPARSE_SLOWLY(name, sample)
 
 //------------------------------------------------------------------------------
+// Histogram instantiation helpers.
+
+// Support a collection of histograms, perhaps one for each entry in an
+// enumeration. This macro manages a block of pointers, adding to a specific
+// one by its index.
+//
+// A typical instantiation looks something like this:
+//  STATIC_HISTOGRAM_POINTER_GROUP(
+//      GetHistogramNameForIndex(histogram_index),
+//      histogram_index, MAXIMUM_HISTOGRAM_INDEX, Add(some_delta),
+//      base::Histogram::FactoryGet(
+//          GetHistogramNameForIndex(histogram_index),
+//          MINIMUM_SAMPLE, MAXIMUM_SAMPLE, BUCKET_COUNT,
+//          base::HistogramBase::kUmaTargetedHistogramFlag));
+//
+// Though it seems inefficient to generate the name twice, the first
+// instance will be used only for DCHECK builds and the second will
+// execute only during the first access to the given index, after which
+// the pointer is cached and the name never needed again.
+#define STATIC_HISTOGRAM_POINTER_GROUP(constant_histogram_name, index,        \
+                                       constant_maximum,                      \
+                                       histogram_add_method_invocation,       \
+                                       histogram_factory_get_invocation)      \
+  do {                                                                        \
+    static base::subtle::AtomicWord atomic_histograms[constant_maximum];      \
+    DCHECK_LE(0, index);                                                      \
+    DCHECK_LT(index, constant_maximum);                                       \
+    HISTOGRAM_POINTER_USE(&atomic_histograms[index], constant_histogram_name, \
+                          histogram_add_method_invocation,                    \
+                          histogram_factory_get_invocation);                  \
+  } while (0)
+
+//------------------------------------------------------------------------------
 // Deprecated histogram macros. Not recommended for current use.
 
 // Legacy name for UMA_HISTOGRAM_COUNTS_1M. Suggest using explicit naming
 // and not using this macro going forward.
 #define UMA_HISTOGRAM_COUNTS(name, sample) UMA_HISTOGRAM_CUSTOM_COUNTS(        \
     name, sample, 1, 1000000, 50)
 
 // MB-granularity memory metric. This has a short max (1G).
 #define UMA_HISTOGRAM_MEMORY_MB(name, sample)                                  \
     UMA_HISTOGRAM_CUSTOM_COUNTS(name, sample, 1, 1000, 50)
 
 // For an enum with customized range. In general, sparse histograms should be
 // used instead.
 // Samples should be one of the std::vector<int> list provided via
 // |custom_ranges|. See comments above CustomRanges::FactoryGet about the
 // requirement of |custom_ranges|. You can use the helper function
 // CustomHistogram::ArrayToCustomRanges to transform a C-style array of valid
 // sample values to a std::vector<int>.
 #define UMA_HISTOGRAM_CUSTOM_ENUMERATION(name, sample, custom_ranges)          \
     STATIC_HISTOGRAM_POINTER_BLOCK(name, Add(sample),                          \
         base::CustomHistogram::FactoryGet(name, custom_ranges,                 \
             base::HistogramBase::kUmaTargetedHistogramFlag))
 
 #endif  // BASE_METRICS_HISTOGRAM_MACROS_H_