add maps and sets to zone containers

src/zone-containers.h

Index: src/zone-containers.h
diff --git a/src/zone-containers.h b/src/zone-containers.h
index de635fde05dda6ef0d4058c63552809a86a0469d..0a599bcf2b0501500fc4a17369728a7660cc8107 100644
--- a/src/zone-containers.h
+++ b/src/zone-containers.h
@@ -7,7 +7,9 @@
 
 #include <deque>
 #include <list>
+#include <map>
 #include <queue>
+#include <set>
 #include <stack>
 #include <vector>
 
@@ -83,6 +85,31 @@ class ZoneStack : public std::stack<T, ZoneDeque<T>> {
 };
 
 
+// A wrapper subclass for std::set to make it easy to construct one that uses
+// a zone allocator.
+template <typename K, typename Compare = std::less<K>>
+class ZoneSet : public std::set<K, Compare, zone_allocator<K>> {
+ public:
+  // Constructs an empty set.
+  explicit ZoneSet(Zone* zone)
+      : std::set<K, Compare, zone_allocator<K>>(Compare(),
+                                                zone_allocator<K>(zone)) {}
+};
+
+
+// A wrapper subclass for std::map to make it easy to construct one that uses
+// a zone allocator.
+template <typename K, typename V, typename Compare = std::less<K>>
+class ZoneMap
+    : public std::map<K, V, Compare, zone_allocator<std::pair<K, V>>> {
+ public:
+  // Constructs an empty map.
+  explicit ZoneMap(Zone* zone)
+      : std::map<K, V, Compare, zone_allocator<std::pair<K, V>>>(
+            Compare(), zone_allocator<std::pair<K, V>>(zone)) {}
+};
+
+
 // Typedefs to shorten commonly used vectors.
 typedef ZoneVector<bool> BoolVector;
 typedef ZoneVector<int> IntVector;