Record call site history in LeakDetectorImpl

components/metrics/leak_detector/ranked_set.h

Index: components/metrics/leak_detector/ranked_set.h
diff --git a/components/metrics/leak_detector/ranked_set.h b/components/metrics/leak_detector/ranked_set.h
index f91251593b046147d5ed2f7ac99f77886ee50235..87c150e38a3ea7135cbd43877c899ae4368fda00 100644
--- a/components/metrics/leak_detector/ranked_set.h
+++ b/components/metrics/leak_detector/ranked_set.h
@@ -72,7 +72,20 @@ class RankedSet {
     Add(ValueType(call_stack), count);
   }
 
+  // Helper functions to directly search for an element with |value| equal to a
+  // particular size or call stack. The time complexity is O(n) rather than the
+  // O(log n) typical of std::set. These should be called sparingly in
+  // performance-critical code.
+  const_iterator FindSize(size_t size) const { return Find(ValueType(size)); }
+  const_iterator FindCallStack(const CallStack* call_stack) const {
+    return Find(ValueType(call_stack));
+  }
+
  private:
+  // Returns an iterator to the element in |entries_| with value=|value|, or to
+  // entries_.end() if it was not found.
+  const_iterator Find(const ValueType& value) const;
+
   // Max and min counts. Returns 0 if the list is empty.
   int max_count() const {
     return entries_.empty() ? 0 : entries_.begin()->count;