Support general expressions as keys in literal maps.

sdk/lib/_internal/lib/js_helper.dart

Index: sdk/lib/_internal/lib/js_helper.dart
diff --git a/sdk/lib/_internal/lib/js_helper.dart b/sdk/lib/_internal/lib/js_helper.dart
index fe0fcc1b7cae1cb4fa568ec23fc95cbf4409f169..7c253ea488540532390ade91c5d46a20aada0d5f 100644
--- a/sdk/lib/_internal/lib/js_helper.dart
+++ b/sdk/lib/_internal/lib/js_helper.dart
@@ -1425,13 +1425,15 @@ class _StackTrace implements StackTrace {
  * Called by generated code to build a map literal. [keyValuePairs] is
  * a list of key, value, key, value, ..., etc.
  */
-makeLiteralMap(List keyValuePairs) {
-  Iterator iterator = keyValuePairs.iterator;
+makeLiteralMap(keyValuePairs) {
+  // TODO(johnniwinther): Use JSArray to optimize this code instead of calling
+  // [getLength] and [getIndex].
   Map result = new LinkedHashMap();
-  while (iterator.moveNext()) {
-    String key = iterator.current;
-    iterator.moveNext();
-    var value = iterator.current;
+  int index = 0;
+  int length = getLength(keyValuePairs);
+  while (index < length) {
+    var key = getIndex(keyValuePairs, index++);
+    var value = getIndex(keyValuePairs, index++);
     result[key] = value;
   }
   return result;