Allocators for map<K, V> need to allocate pair<const K, V>.

BUG=chromium:562227
LOG=n

Review URL: https://codereview.chromium.org/1479893002

Cr-Commit-Position: refs/heads/master@{#32360}

src/compiler/instruction.h

@@ -1083,7 +1083,7 @@ class InstructionBlock final : public ZoneObject {
 
 typedef ZoneDeque<Constant> ConstantDeque;
 typedef std::map<int, Constant, std::less<int>,
-                 zone_allocator<std::pair<int, Constant> > > ConstantMap;
+                 zone_allocator<std::pair<const int, Constant> > > ConstantMap;
 
 typedef ZoneDeque<Instruction*> InstructionDeque;
 typedef ZoneDeque<ReferenceMap*> ReferenceMapDeque;

src/zone-containers.h

@@ -114,12 +114,12 @@ class ZoneSet : public std::set<K, Compare, zone_allocator<K>> {
 // 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 std::map<K, V, Compare, zone_allocator<std::pair<const 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)) {}
+      : std::map<K, V, Compare, zone_allocator<std::pair<const K, V>>>(
+            Compare(), zone_allocator<std::pair<const K, V>>(zone)) {}
 };