Fix overflow when logging MaxInt32 to a sparse histogram.

base/metrics/persistent_sample_map.cc

Index: base/metrics/persistent_sample_map.cc
diff --git a/base/metrics/persistent_sample_map.cc b/base/metrics/persistent_sample_map.cc
index dd5b8320c16dafafb49d74057883503af3e3fbaa..0b880079401946b8b867f9fa671c73ba82cf89a7 100644
--- a/base/metrics/persistent_sample_map.cc
+++ b/base/metrics/persistent_sample_map.cc
@@ -41,7 +41,7 @@ class PersistentSampleMapIterator : public SampleCountIterator {
   bool Done() const override;
   void Next() override;
   void Get(HistogramBase::Sample* min,
-           HistogramBase::Sample* max,
+           int64_t* max,
            HistogramBase::Count* count) const override;
 
  private:
@@ -71,13 +71,13 @@ void PersistentSampleMapIterator::Next() {
 }
 
 void PersistentSampleMapIterator::Get(Sample* min,
-                                      Sample* max,
+                                      int64_t* max,
                                       Count* count) const {
   DCHECK(!Done());
   if (min)
     *min = iter_->first;
   if (max)
-    *max = iter_->first + 1;
+    *max = static_cast<int64_t>(iter_->first) + 1;

[Ilya Sherman, 2017/05/02 21:37:49]

nit: Here and everywhere else that you add a static_cast, could you please use a
strict_cast from base/numerics/safe_conversions.h instead?

[Alexei Svitkine (slow), 2017/05/03 15:21:53]

Done.

   if (count)
     *count = *iter_->second;
 }
@@ -186,13 +186,13 @@ PersistentSampleMap::CreatePersistentRecord(
 bool PersistentSampleMap::AddSubtractImpl(SampleCountIterator* iter,
                                           Operator op) {
   Sample min;
-  Sample max;
+  int64_t max;
   Count count;
   for (; !iter->Done(); iter->Next()) {
     iter->Get(&min, &max, &count);
     if (count == 0)
       continue;
-    if (min + 1 != max)
+    if (static_cast<int64_t>(min) + 1 != max)
       return false;  // SparseHistogram only supports bucket with size 1.
 
 #if 0  // TODO(bcwhite) Re-enable efficient version after crbug.com/682680.