Reduce histogram creation time by avoiding import of those just created.

base/metrics/histogram_unittest.cc

 // Copyright (c) 2012 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 "base/metrics/histogram.h"
 
 #include <limits.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 691 matching lines @@
   // Create all histogram names in advance for accurate timing below.
   std::vector<std::string> histogram_names;
   for (int i = 0; i < kTestCreateCount; ++i) {
     histogram_names.push_back(
         StringPrintf("TestHistogram.%d", i % kTestCreateCount));
   }
 
   // Calculate cost of creating histograms.
   TimeTicks create_start = TimeTicks::Now();
   for (int i = 0; i < kTestCreateCount; ++i) {
-    Histogram::FactoryGet(histogram_names[i], 0, 100, 10,
+    Histogram::FactoryGet(histogram_names[i], 1, 100, 10,
                           HistogramBase::kNoFlags);
   }
   TimeDelta create_ticks = TimeTicks::Now() - create_start;
   int64_t create_ms = create_ticks.InMilliseconds();
 
   VLOG(1) << kTestCreateCount << " histogram creations took " << create_ms
           << "ms or about "
           << (create_ms * 1000000) / kTestCreateCount
           << "ns each.";
 
   // Calculate cost of looking up existing histograms.
   TimeTicks lookup_start = TimeTicks::Now();
   for (int i = 0; i < kTestLookupCount; ++i) {
     // 6007 is co-prime with kTestCreateCount and so will do lookups in an
     // order less likely to be cacheable (but still hit them all) should the
     // underlying storage use the exact histogram name as the key.
     const int i_mult = 6007;
     static_assert(i_mult < INT_MAX / kTestCreateCount, "Multiplier too big");
     int index = (i * i_mult) & (kTestCreateCount - 1);
-    Histogram::FactoryGet(histogram_names[index], 0, 100, 10,
+    Histogram::FactoryGet(histogram_names[index], 1, 100, 10,
                           HistogramBase::kNoFlags);
   }
   TimeDelta lookup_ticks = TimeTicks::Now() - lookup_start;
   int64_t lookup_ms = lookup_ticks.InMilliseconds();
 
   VLOG(1) << kTestLookupCount << " histogram lookups took " << lookup_ms
           << "ms or about "
           << (lookup_ms * 1000000) / kTestLookupCount
           << "ns each.";
 
   // Calculate cost of accessing histograms.
   HistogramBase* histogram = Histogram::FactoryGet(
-      histogram_names[0], 0, 100, 10, HistogramBase::kNoFlags);
+      histogram_names[0], 1, 100, 10, HistogramBase::kNoFlags);
   ASSERT_TRUE(histogram);
   TimeTicks add_start = TimeTicks::Now();
   for (int i = 0; i < kTestAddCount; ++i)
     histogram->Add(i & 127);
   TimeDelta add_ticks = TimeTicks::Now() - add_start;
   int64_t add_ms = add_ticks.InMilliseconds();
 
   VLOG(1) << kTestAddCount << " histogram adds took " << add_ms
           << "ms or about "
           << (add_ms * 1000000) / kTestAddCount
@@ skipping 41 matching lines @@
   // CustomHistogram needs at least 1 valid range.
   custom_ranges.clear();
   custom_ranges.push_back(0);
   EXPECT_DEATH(CustomHistogram::FactoryGet("BadRangesCustom3", custom_ranges,
                                            HistogramBase::kNoFlags),
                "");
 }
 #endif
 
 }  // namespace base