Return a NULL histogram pointer on construction error

base/metrics/histogram.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.
 
 // Histogram is an object that aggregates statistics, and can summarize them in
 // various forms, including ASCII graphical, HTML, and numerically (as a
 // vector of numbers corresponding to each of the aggregating buckets).
 // See header file for details and examples.
 
 #include "base/metrics/histogram.h"
@@ skipping 58 matching lines @@
 }
 
 bool ValidateRangeChecksum(const HistogramBase& histogram,
                            uint32 range_checksum) {
   const Histogram& casted_histogram =
       static_cast<const Histogram&>(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 {
+    return false;
+  }
+
+  DummyHistogram() : Histogram("Dummy", 0, 1, NULL) {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(DummyHistogram);
+};
+
 }  // namespace
 
 typedef HistogramBase::Count Count;
 typedef HistogramBase::Sample Sample;
 
 // static
 const size_t Histogram::kBucketCount_MAX = 16384u;
 
 HistogramBase* Histogram::FactoryGet(const string& name,
                                      Sample minimum,
                                      Sample maximum,
                                      size_t bucket_count,
-                                     int32 flags) {
+                                     int32 flags,
+                                     int32 construction_behavior) {
   bool valid_arguments =
       InspectConstructionArguments(name, &minimum, &maximum, &bucket_count);
   DCHECK(valid_arguments);
 
   HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
   if (!histogram) {
     // To avoid racy destruction at shutdown, the following will be leaked.
     BucketRanges* ranges = new BucketRanges(bucket_count + 1);
     InitializeBucketRanges(minimum, maximum, ranges);
     const BucketRanges* registered_ranges =
         StatisticsRecorder::RegisterOrDeleteDuplicateRanges(ranges);
 
     Histogram* tentative_histogram =
         new Histogram(name, minimum, maximum, registered_ranges);
 
     tentative_histogram->SetFlags(flags);
     histogram =
         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
   }
 
   DCHECK_EQ(HISTOGRAM, histogram->GetHistogramType());
-  CHECK(histogram->HasConstructionArguments(minimum, maximum, bucket_count));
+  if (construction_behavior == kAllowBadConstruction) {
+    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);
+    }
+  } else {
+    CHECK(histogram->HasConstructionArguments(minimum, maximum, bucket_count));
+  }
   return histogram;
 }
 
 HistogramBase* Histogram::FactoryTimeGet(const string& name,
                                          TimeDelta minimum,
                                          TimeDelta maximum,
                                          size_t bucket_count,
-                                         int32 flags) {
+                                         int32 flags,
+                                         int32 construction_behavior) {
   return FactoryGet(name, minimum.InMilliseconds(), maximum.InMilliseconds(),
-                    bucket_count, flags);
+                    bucket_count, flags, construction_behavior);
 }
 
 TimeTicks Histogram::DebugNow() {
 #ifndef NDEBUG
   return TimeTicks::Now();
 #else
   return TimeTicks();
 #endif
 }
 
@@ skipping 376 matching lines @@
 // LinearHistogram: This histogram uses a traditional set of evenly spaced
 // buckets.
 //------------------------------------------------------------------------------
 
 LinearHistogram::~LinearHistogram() {}
 
 HistogramBase* LinearHistogram::FactoryGet(const string& name,
                                            Sample minimum,
                                            Sample maximum,
                                            size_t bucket_count,
-                                           int32 flags) {
+                                           int32 flags,
+                                           int32 construction_behavior) {
   return FactoryGetWithRangeDescription(
-      name, minimum, maximum, bucket_count, flags, NULL);
+      name, minimum, maximum, bucket_count, flags, NULL, construction_behavior);
 }
 
 HistogramBase* LinearHistogram::FactoryTimeGet(const string& name,
                                                TimeDelta minimum,
                                                TimeDelta maximum,
                                                size_t bucket_count,
-                                               int32 flags) {
+                                               int32 flags,
+                                               int32 construction_behavior) {
   return FactoryGet(name, minimum.InMilliseconds(), maximum.InMilliseconds(),
-                    bucket_count, flags);
+                    bucket_count, flags, construction_behavior);
 }
 
 HistogramBase* LinearHistogram::FactoryGetWithRangeDescription(
       const std::string& name,
       Sample minimum,
       Sample maximum,
       size_t bucket_count,
       int32 flags,
-      const DescriptionPair descriptions[]) {
+      const DescriptionPair descriptions[],
+      int32 construction_behavior) {
   bool valid_arguments = Histogram::InspectConstructionArguments(
       name, &minimum, &maximum, &bucket_count);
   DCHECK(valid_arguments);
 
   HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
   if (!histogram) {
     // To avoid racy destruction at shutdown, the following will be leaked.
     BucketRanges* ranges = new BucketRanges(bucket_count + 1);
     InitializeBucketRanges(minimum, maximum, ranges);
     const BucketRanges* registered_ranges =
         StatisticsRecorder::RegisterOrDeleteDuplicateRanges(ranges);
 
     LinearHistogram* tentative_histogram =
         new LinearHistogram(name, minimum, maximum, registered_ranges);
 
     // Set range descriptions.
     if (descriptions) {
       for (int i = 0; descriptions[i].description; ++i) {
         tentative_histogram->bucket_description_[descriptions[i].sample] =
             descriptions[i].description;
       }
     }
 
     tentative_histogram->SetFlags(flags);
     histogram =
         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
   }
 
   DCHECK_EQ(LINEAR_HISTOGRAM, histogram->GetHistogramType());
-  CHECK(histogram->HasConstructionArguments(minimum, maximum, bucket_count));
+  if (construction_behavior == kAllowBadConstruction) {
+    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);
+    }
+  } else {
+    CHECK(histogram->HasConstructionArguments(minimum, maximum, bucket_count));
+  }
   return histogram;
 }
 
 HistogramType LinearHistogram::GetHistogramType() const {
   return LINEAR_HISTOGRAM;
 }
 
 LinearHistogram::LinearHistogram(const string& name,
                                  Sample minimum,
                                  Sample maximum,
@@ skipping 244 matching lines @@
 
   BucketRanges* bucket_ranges = new BucketRanges(ranges.size());
   for (size_t i = 0; i < ranges.size(); i++) {
     bucket_ranges->set_range(i, ranges[i]);
   }
   bucket_ranges->ResetChecksum();
   return bucket_ranges;
 }
 
 }  // namespace base