Add a new node in the inferrer to materialize literal maps.

sdk/lib/_internal/compiler/implementation/inferrer/inferrer_visitor.dart

Index: sdk/lib/_internal/compiler/implementation/inferrer/inferrer_visitor.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/inferrer/inferrer_visitor.dart	(revision 30992)
+++ sdk/lib/_internal/compiler/implementation/inferrer/inferrer_visitor.dart	(working copy)
@@ -42,11 +42,13 @@
   bool isNull(T type);
   Selector newTypedSelector(T receiver, Selector selector);
 
-  T allocateContainer(T type,
-                      Node node,
-                      Element enclosing,
-                      [T elementType, int length]);
+  T allocateList(T type,
+                 Node node,
+                 Element enclosing,
+                 [T elementType, int length]);
 
+  T allocateMap(T keyType, T valueType, T type);
+
   /**
    * Returns the least upper bound between [firstType] and
    * [secondType].