Fix overflow when logging MaxInt32 to a sparse histogram.

base/metrics/sample_map.cc

Index: base/metrics/sample_map.cc
diff --git a/base/metrics/sample_map.cc b/base/metrics/sample_map.cc
index 5ef0fb87ab604d23a5bdb203e774247c69c62257..f6f2e45e8c779daea5c48ef3cb0e85001d0b96ef 100644
--- a/base/metrics/sample_map.cc
+++ b/base/metrics/sample_map.cc
@@ -30,7 +30,7 @@ class SampleMapIterator : 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:
@@ -58,12 +58,12 @@ void SampleMapIterator::Next() {
   SkipEmptyBuckets();
 }
 
-void SampleMapIterator::Get(Sample* min, Sample* max, Count* count) const {
+void SampleMapIterator::Get(Sample* min, 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;
   if (count)
     *count = iter_->second;
 }
@@ -108,11 +108,11 @@ std::unique_ptr<SampleCountIterator> SampleMap::Iterator() const {
 
 bool SampleMap::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 (min + 1 != max)
+    if (static_cast<int64_t>(min) + 1 != max)
       return false;  // SparseHistogram only supports bucket with size 1.
 
     sample_counts_[min] += (op == HistogramSamples::ADD) ? count : -count;