Support new import syntax.

lib/compiler/implementation/tree/unparser.dart

Index: lib/compiler/implementation/tree/unparser.dart
diff --git a/lib/compiler/implementation/tree/unparser.dart b/lib/compiler/implementation/tree/unparser.dart
index a52545f076648f006c2deb06f738fdb524dcf9ea..c9f166582f0a5c676b5b629158333224195c8d32 100644
--- a/lib/compiler/implementation/tree/unparser.dart
+++ b/lib/compiler/implementation/tree/unparser.dart
@@ -443,8 +443,8 @@ class Unparser implements Visitor {
   }
 
   unparseImportTag(String uri, [String prefix]) {
-    final suffix = prefix === null ? '' : ',prefix:"$prefix"';
-    sb.add('#import("$uri"$suffix);');
+    final suffix = prefix === null ? '' : ' as $prefix';
+    sb.add('import "$uri"$suffix;');
   }
 
   visitScriptTag(ScriptTag node) {