Correctly handle constness for list and map literals inside bodies.

lib/compiler/implementation/tree/nodes.dart

Index: lib/compiler/implementation/tree/nodes.dart
diff --git a/lib/compiler/implementation/tree/nodes.dart b/lib/compiler/implementation/tree/nodes.dart
index 6b489f4eea5ca4240047a5270c7a042daa22b5ce..01f6cf276062779a1750bbb180ac2eb2476892ad 100644
--- a/lib/compiler/implementation/tree/nodes.dart
+++ b/lib/compiler/implementation/tree/nodes.dart
@@ -1220,9 +1220,11 @@ class LiteralMap extends Expression {
   final NodeList typeArguments;
   final NodeList entries;
 
-  LiteralMap(this.typeArguments, this.entries);
+  final Token constKeyword;
+
+  LiteralMap(this.typeArguments, this.entries, this.constKeyword);
 
-  bool isConst() => false; // TODO(ahe): Store constness.
+  bool isConst() => constKeyword !== null;
 
   LiteralMap asLiteralMap() => this;
 
@@ -1233,7 +1235,10 @@ class LiteralMap extends Expression {
     entries.accept(visitor);
   }
 
-  Token getBeginToken() => firstBeginToken(typeArguments, entries);
+  Token getBeginToken() {
+    if (constKeyword !== null) return constKeyword;
+    return firstBeginToken(typeArguments, entries);
+  }
 
   Token getEndToken() => entries.getEndToken();
 }