Return a NULL histogram pointer on construction error

chrome/browser/extensions/api/metrics_private/metrics_apitest.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 <map>
 
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/metrics/user_metrics.h"
@@ skipping 15 matching lines @@
 
 // The tests that are run by this extension are expected to record the following
 // histograms.  If the tests in test.js are modified, this array may need to be
 // updated.
 struct RecordedHistogram {
   const char* name;
   base::HistogramType type;
   int min;
   int max;
   size_t buckets;
+  int count;
 } g_histograms[] = {
-  {"test.h.1", base::HISTOGRAM, 1, 100, 50},  // custom
-  {"test.h.2", base::LINEAR_HISTOGRAM, 1, 200, 50},  // custom
-  {"test.h.3", base::LINEAR_HISTOGRAM, 1, 101, 102},  // percentage
-  {"test.time", base::HISTOGRAM, 1, 10000, 50},
-  {"test.medium.time", base::HISTOGRAM, 1, 180000, 50},
-  {"test.long.time", base::HISTOGRAM, 1, 3600000, 50},
-  {"test.count", base::HISTOGRAM, 1, 1000000, 50},
-  {"test.medium.count", base::HISTOGRAM, 1, 10000, 50},
-  {"test.small.count", base::HISTOGRAM, 1, 100, 50},
+  {"test.h.1", base::HISTOGRAM, 1, 100, 50, 1},  // custom
+  {"test.h.2", base::LINEAR_HISTOGRAM, 1, 200, 50, 1},  // custom
+  {"test.h.3", base::LINEAR_HISTOGRAM, 1, 101, 102, 2},  // percentage
+  {"test.time", base::HISTOGRAM, 1, 10000, 50, 1},
+  {"test.medium.time", base::HISTOGRAM, 1, 180000, 50, 1},
+  {"test.long.time", base::HISTOGRAM, 1, 3600000, 50, 1},
+  {"test.count", base::HISTOGRAM, 1, 1000000, 50, 1},
+  {"test.medium.count", base::HISTOGRAM, 1, 10000, 50, 1},
+  {"test.small.count", base::HISTOGRAM, 1, 100, 50, 1},
+  {"test.bucketchange.linear", base::LINEAR_HISTOGRAM, 1, 100, 10, 2},

[Alexei Svitkine (slow), 2014/01/17 15:40:13]

Can you also add tests for this to histogram_unittest.cc?

[elijahtaylor1, 2014/01/17 20:04:16]

Done.

+  {"test.bucketchange.log", base::HISTOGRAM, 1, 100, 10, 2},
 };
 
 // This class observes and collects user action notifications that are sent
 // by the tests, so that they can be examined afterwards for correctness.
 class UserActionObserver {
  public:
   UserActionObserver();
   ~UserActionObserver();
 
   void ValidateUserActions(const RecordedUserAction* recorded, int count);
@@ skipping 53 matching lines @@
   for (int i = 0; i < count; ++i) {
     const RecordedHistogram& r = recorded[i];
     size_t j = 0;
     for (j = 0; j < histograms.size(); ++j) {
       base::HistogramBase* histogram(histograms[j]);
 
       if (r.name == histogram->histogram_name()) {
         EXPECT_EQ(r.type, histogram->GetHistogramType());
         EXPECT_TRUE(
             histogram->HasConstructionArguments(r.min, r.max, r.buckets));
+        scoped_ptr<base::HistogramSamples> snapshot =
+            histogram->SnapshotSamples();
+        base::HistogramBase::Count sample_count = snapshot->TotalCount();
+        EXPECT_EQ(sample_count, r.count);
         break;
       }
     }
     EXPECT_LT(j, histograms.size());
   }
 }
 
 }  // anonymous namespace
 
 IN_PROC_BROWSER_TEST_F(ExtensionApiTest, Metrics) {
   UserActionObserver observer;
 
   base::FieldTrialList::CreateFieldTrial("apitestfieldtrial2", "group1");
 
   std::map<std::string, std::string> params;
   params["a"] = "aa";
   params["b"] = "bb";
   ASSERT_TRUE(chrome_variations::AssociateVariationParams(
       "apitestfieldtrial2", "group1", params));
 
   ASSERT_TRUE(RunComponentExtensionTest("metrics")) << message_;
 
   observer.ValidateUserActions(g_user_actions, arraysize(g_user_actions));
   ValidateHistograms(g_histograms, arraysize(g_histograms));
 }