Implement tracking of BUILD.gn files used to define target, toolchain or

base/containers/flat_tree.h

Index: base/containers/flat_tree.h
diff --git a/base/containers/flat_tree.h b/base/containers/flat_tree.h
index afbbf95c4fdda48db3065cb86c202c9ef169e1f6..8bbd3007739aff77bc184f1aa9c97294dbd1039c 100644
--- a/base/containers/flat_tree.h
+++ b/base/containers/flat_tree.h
@@ -124,18 +124,18 @@ class flat_tree {
   template <class InputIterator>
   flat_tree(InputIterator first,
             InputIterator last,
-            FlatContainerDupes dupe_handling,
+            FlatContainerDupes dupe_handling = KEEP_FIRST_OF_DUPES,
             const key_compare& comp = key_compare());
 
   flat_tree(const flat_tree&);
   flat_tree(flat_tree&&);
 
   flat_tree(std::vector<value_type> items,
-            FlatContainerDupes dupe_handling,
+            FlatContainerDupes dupe_handling = KEEP_FIRST_OF_DUPES,
             const key_compare& comp = key_compare());
 
   flat_tree(std::initializer_list<value_type> ilist,
-            FlatContainerDupes dupe_handling,
+            FlatContainerDupes dupe_handling = KEEP_FIRST_OF_DUPES,
             const key_compare& comp = key_compare());
 
   ~flat_tree();
@@ -215,7 +215,7 @@ class flat_tree {
   template <class InputIterator>
   void insert(InputIterator first,
               InputIterator last,
-              FlatContainerDupes dupes);
+              FlatContainerDupes dupes = KEEP_FIRST_OF_DUPES);
 
   template <class... Args>
   std::pair<iterator, bool> emplace(Args&&... args);