Support defining environment constants for dart2js via the command-line.

sdk/lib/_internal/pub/lib/src/utils.dart

Index: sdk/lib/_internal/pub/lib/src/utils.dart
diff --git a/sdk/lib/_internal/pub/lib/src/utils.dart b/sdk/lib/_internal/pub/lib/src/utils.dart
index 14d81a67a4138ea4e2c6aac75429c1a6cc05a132..c51202c637e2c6f6b07040351c6b5767cc7e1aeb 100644
--- a/sdk/lib/_internal/pub/lib/src/utils.dart
+++ b/sdk/lib/_internal/pub/lib/src/utils.dart
@@ -371,6 +371,20 @@ Future<Map> mapFromIterableAsync(Iterable iter, {key(element),
   })).then((_) => map);
 }
 
+/// Returns a new map with all values in both [map1] and [map2].

[Bob Nystrom, 2015/04/24 21:33:09]

"values" -> "entries".

[nweiz, 2015/04/24 21:38:06]

Done.

+///
+/// If there are conflicting keys, [map2]'s value wins.

[Bob Nystrom, 2015/04/24 21:33:10]

"conflicting" -> "overlapping".

[nweiz, 2015/04/24 21:38:06]

Done.

+Map mergeMaps(Map map1, Map map2) {
+  var result = {};

[Bob Nystrom, 2015/04/24 21:33:10]

result.addAll(map1);
result.addAll(map2);

[nweiz, 2015/04/24 21:38:06]

Done.

+  map1.forEach((key, value) {
+    result[key] = value;
+  });
+  map2.forEach((key, value) {
+    result[key] = value;
+  });
+  return result;
+}
+
 /// Returns the transitive closure of [graph].
 ///
 /// This assumes [graph] represents a graph with a vertex for each key and an