Rework UMAHistogramHelper and StatisticsDeltaReader into [Chrome]HistogramTester.

chrome/renderer/net/net_error_helper_core_unittest.cc

Index: chrome/renderer/net/net_error_helper_core_unittest.cc
diff --git a/chrome/renderer/net/net_error_helper_core_unittest.cc b/chrome/renderer/net/net_error_helper_core_unittest.cc
index eee80f712388fc78e363f183f4399512b0480de5..c6a0bcb6f73a899deab020a54f573a6c6e7dde06 100644
--- a/chrome/renderer/net/net_error_helper_core_unittest.cc
+++ b/chrome/renderer/net/net_error_helper_core_unittest.cc
@@ -17,7 +17,7 @@
 #include "base/timer/timer.h"
 #include "base/values.h"
 #include "chrome/common/net/net_error_info.h"
-#include "chrome/test/base/uma_histogram_helper.h"
+#include "chrome/test/base/chrome_histogram_tester.h"
 #include "content/public/common/url_constants.h"
 #include "net/base/net_errors.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -2230,37 +2230,15 @@ TEST_F(NetErrorHelperCoreAutoReloadTest, ShownWhileNotReloading) {
   EXPECT_TRUE(timer()->IsRunning());
 }
 
-// Return the count for the named histogram, or 0 if there is no histogram by
-// that name. This function is error-tolerant because histograms that have no
-// data points may not be registered, and the unit tests below still need to be
-// able to check that they haven't changed.
-int GetHistogramCount(const char *name) {
-  base::HistogramBase* histogram =
-      base::StatisticsRecorder::FindHistogram(name);
-  if (!histogram)
-    return 0;
-  scoped_ptr<base::HistogramSamples> samples = histogram->SnapshotSamples();
-  if (!samples)
-    return 0;
-  return samples->TotalCount();
-}
-
-void ExpectHistogramDelta(const char *name, int old_count, int delta) {
-  int new_count = GetHistogramCount(name);
-  EXPECT_EQ(old_count + delta, new_count) << "For histogram " << name;
-}
-
 class NetErrorHelperCoreHistogramTest
     : public NetErrorHelperCoreAutoReloadTest {
  public:
   virtual void SetUp() OVERRIDE {
     NetErrorHelperCoreAutoReloadTest::SetUp();
-    StoreOldCounts();
   }
 
   void ExpectDelta(const char *name, int delta) {
-    DCHECK(old_counts_.count(name) == 1);
-    ExpectHistogramDelta(name, old_counts_[name], delta);
+    histogram_tester_.ExpectTotalCount(name, delta);
   }

[Ilya Sherman, 2014/07/15 03:56:35]

nit: Please inline the calls to histogram_tester_.ExpectTotalCount() rather than
having this wrapper method.

[Mike Lerman, 2014/07/16 17:29:04]

Done.

 
   static const char kCountAtStop[];
@@ -2270,14 +2248,7 @@ class NetErrorHelperCoreHistogramTest
   static const char kErrorAtFirstSuccess[];
 
  private:

[Ilya Sherman, 2014/07/15 03:56:35]

Note: There's no need to make the HistogramTester private if you'd just make a
protected (or public) accessor -- for FooTest classes, it's quite common to have
protected data members to limit boiler plate code.

[Mike Lerman, 2014/07/16 17:29:04]

It can stay private.

-  void StoreOldCounts() {
-    for (size_t i = 0; kHistogramNames[i]; i++)
-      old_counts_[kHistogramNames[i]] = GetHistogramCount(kHistogramNames[i]);
-  }
-
-  static const char *kHistogramNames[];
-
-  std::map<std::string, int> old_counts_;
+  base::HistogramTester histogram_tester_;
 };
 
 const char NetErrorHelperCoreHistogramTest::kCountAtStop[] =
@@ -2290,14 +2261,6 @@ const char NetErrorHelperCoreHistogramTest::kErrorAtSuccess[] =
     "Net.AutoReload.ErrorAtSuccess";
 const char NetErrorHelperCoreHistogramTest::kErrorAtFirstSuccess[] =
     "Net.AutoReload.ErrorAtFirstSuccess";
-const char *NetErrorHelperCoreHistogramTest::kHistogramNames[] = {
-  kCountAtStop,
-  kErrorAtStop,
-  kCountAtSuccess,
-  kErrorAtSuccess,
-  kErrorAtFirstSuccess,
-  NULL
-};
 
 // Test that the success histograms are updated when auto-reload succeeds at the
 // first attempt, and that the failure histograms are not updated.