Return a NULL histogram pointer on construction error

base/metrics/histogram.cc

Index: base/metrics/histogram.cc
diff --git a/base/metrics/histogram.cc b/base/metrics/histogram.cc
index fbe66d05d29fd3c2896f8499dd1dc07d9793d095..0a56174bfeeac60ecdb4488b3e58984005d5e700 100644
--- a/base/metrics/histogram.cc
+++ b/base/metrics/histogram.cc
@@ -76,6 +76,27 @@ bool ValidateRangeChecksum(const HistogramBase& histogram,
   return casted_histogram.bucket_ranges()->checksum() == range_checksum;
 }
 
+// DummyHistogram is an object that overrides Histogram's Add* functions
+// to provide no functionality. This can be returned in the case of mismatched
+// construction arguments to any of the other Histograms' FactoryGet calls.
+class DummyHistogram : public Histogram {
+ public:
+  virtual void Add(Sample value) OVERRIDE {}
+  virtual void AddSamples(const HistogramSamples& samples) OVERRIDE {}
+  virtual bool AddSamplesFromPickle(PickleIterator* iter) OVERRIDE;
+
+  DummyHistogram();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(DummyHistogram);
+};
+
+bool DummyHistogram::AddSamplesFromPickle(PickleIterator* iter) {

[Alexei Svitkine (slow), 2014/01/17 20:06:31]

Nit: You can probably define these inline above.

[elijahtaylor1, 2014/01/17 20:25:34]

I got an error on some windows trybots before for inlining non-empty functions. 
Is that only in header files?

[Alexei Svitkine (slow), 2014/01/17 22:14:27]

I think it should work - there's code elsewhere that does this. What's the
error?

+  return false;
+}
+
+DummyHistogram::DummyHistogram() : Histogram("Dummy", 0, 1, NULL) {}
+
 }  // namespace
 
 typedef HistogramBase::Count Count;
@@ -110,7 +131,16 @@ HistogramBase* Histogram::FactoryGet(const string& name,
   }
 
   DCHECK_EQ(HISTOGRAM, histogram->GetHistogramType());
-  CHECK(histogram->HasConstructionArguments(minimum, maximum, bucket_count));
+  if (!histogram->HasConstructionArguments(minimum, maximum, bucket_count)) {
+    // The construction arguments do not match the existing histogram.  This can
+    // come about if an extension updates in the middle of a chrome run and has
+    // changed one of them.  We return a dummy object here instead of crashing
+    // so poor use of extension/Pepper APIs do not cause crashes in Chrome.
+    DLOG(ERROR) << "Histogram " << name << " has bad construction arguments";
+    DummyHistogram* tentative_histogram = new DummyHistogram;
+    histogram =
+        StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
+  }
   return histogram;
 }
 
@@ -567,7 +597,16 @@ HistogramBase* LinearHistogram::FactoryGetWithRangeDescription(
   }
 
   DCHECK_EQ(LINEAR_HISTOGRAM, histogram->GetHistogramType());
-  CHECK(histogram->HasConstructionArguments(minimum, maximum, bucket_count));
+  if (!histogram->HasConstructionArguments(minimum, maximum, bucket_count)) {
+    // The construction arguments do not match the existing histogram.  This can
+    // come about if an extension updates in the middle of a chrome run and has
+    // changed one of them.  We return a dummy object here instead of crashing
+    // so poor use of extension/Pepper APIs do not cause crashes in Chrome.
+    DLOG(ERROR) << "Histogram " << name << " has bad construction arguments";
+    DummyHistogram* tentative_histogram = new DummyHistogram;
+    histogram =
+        StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
+  }
   return histogram;
 }