Record call site history in LeakDetectorImpl

components/metrics/leak_detector/ranked_set.cc

Index: components/metrics/leak_detector/ranked_set.cc
diff --git a/components/metrics/leak_detector/ranked_set.cc b/components/metrics/leak_detector/ranked_set.cc
index 5725fb5c01c83cb6f2a0c456096402375c032355..d2cbd64e15d50deb17c60c60d96789f6330682c6 100644
--- a/components/metrics/leak_detector/ranked_set.cc
+++ b/components/metrics/leak_detector/ranked_set.cc
@@ -48,5 +48,17 @@ void RankedSet::Add(const ValueType& value, int count) {
     entries_.erase(--entries_.end());
 }
 
+RankedSet::const_iterator RankedSet::Find(const ValueType& value) const {
+  // Due to the unusual way the entries are stored, it is best to manually
+  // iterate through them until an entry with a matching value is found.
+  // e.g. std::find() would not work because it depends on exact matching by the
+  // whole Entry struct.
+  for (const_iterator iter = begin(); iter != end(); ++iter) {
+    if (iter->value == value)
+      return iter;
+  }
+  return end();
+}
+
 }  // namespace leak_detector
 }  // namespace metrics