Implement type checking of map literals (issue 221).

runtime/lib/immutable_map.dart

Index: runtime/lib/immutable_map.dart
===================================================================
--- runtime/lib/immutable_map.dart	(revision 1763)
+++ runtime/lib/immutable_map.dart	(working copy)
@@ -93,16 +93,3 @@
   }
 }
 
-
-class MutableMap {
-  // [elements] contains n key-value pairs. The keys are at position
-  // 2*n, the values at position 2*n+1.
-  static fromLiteral(List elements) {
-    var map = new LinkedHashMap();
-    var len = elements.length;
-    for (int i = 1; i < len; i += 2) {
-      map[elements[i-1]] = elements[i];
-    }
-    return map;
-  }
-}