Cache the ranges_ vector and share the ranges_ vector

base/metrics/histogram_unittest.cc

Index: base/metrics/histogram_unittest.cc
===================================================================
--- base/metrics/histogram_unittest.cc	(revision 106341)
+++ base/metrics/histogram_unittest.cc	(working copy)
@@ -387,25 +387,26 @@
   EXPECT_EQ(Histogram::NO_INCONSISTENCIES, 0);
   EXPECT_EQ(0, histogram->FindCorruption(snapshot));  // No default corruption.
 
-  std::swap(histogram->ranges_[1], histogram->ranges_[2]);
+  CachedRanges* cached_ranges = histogram->cached_ranges();
+  std::swap(cached_ranges->ranges_[1], cached_ranges->ranges_[2]);
   EXPECT_EQ(Histogram::BUCKET_ORDER_ERROR | Histogram::RANGE_CHECKSUM_ERROR,
             histogram->FindCorruption(snapshot));
 
-  std::swap(histogram->ranges_[1], histogram->ranges_[2]);
+  std::swap(cached_ranges->ranges_[1], cached_ranges->ranges_[2]);
   EXPECT_EQ(0, histogram->FindCorruption(snapshot));
 
-  ++histogram->ranges_[3];
+  ++cached_ranges->ranges_[3];
   EXPECT_EQ(Histogram::RANGE_CHECKSUM_ERROR,
             histogram->FindCorruption(snapshot));
 
   // Show that two simple changes don't offset each other
-  --histogram->ranges_[4];
+  --cached_ranges->ranges_[4];
   EXPECT_EQ(Histogram::RANGE_CHECKSUM_ERROR,
             histogram->FindCorruption(snapshot));
 
   // Repair histogram so that destructor won't DCHECK().
-  --histogram->ranges_[3];
-  ++histogram->ranges_[4];
+  --cached_ranges->ranges_[3];
+  ++cached_ranges->ranges_[4];
 }
 
 // Table was generated similarly to sample code for CRC-32 given on:
@@ -424,4 +425,29 @@
   }
 }
 
+// RangeTest, CustomRangeTest and CorruptBucketBounds test CachedRanges class.
+// The following tests sharing of CachedRanges object.
+TEST(HistogramTest, CachedRangesTest) {
+  StatisticsRecorder recorder;
+  StatisticsRecorder::Histograms histograms;
+
+  recorder.GetHistograms(&histograms);
+  EXPECT_EQ(0U, histograms.size());
+
+  Histogram* histogram1(Histogram::FactoryGet(
+      "Histogram", 1, 64, 8, Histogram::kNoFlags));
+
+  Histogram* histogram2(Histogram::FactoryGet(
+      "Histogram2", 1, 64, 8, Histogram::kNoFlags));
+
+  Histogram* histogram3(Histogram::FactoryGet(
+      "Histogram3", 1, 64, 16, Histogram::kNoFlags));
+
+  CachedRanges* cached_ranges1 = histogram1->cached_ranges();
+  CachedRanges* cached_ranges2 = histogram2->cached_ranges();
+  CachedRanges* cached_ranges3 = histogram3->cached_ranges();
+  EXPECT_TRUE(cached_ranges1->Equals(cached_ranges2));
+  EXPECT_FALSE(cached_ranges1->Equals(cached_ranges3));
+}
+
 }  // namespace base