Change Maps to HashMaps to save in performance, index and generated directories not touched

pkg/analysis_server/test/package_uri_resolver_test.dart

Index: pkg/analysis_server/test/package_uri_resolver_test.dart
diff --git a/pkg/analysis_server/test/package_uri_resolver_test.dart b/pkg/analysis_server/test/package_uri_resolver_test.dart
index f059fdc086091b02675de211ac9ef123b7f994e8..e9c6e281ab04f5f61396a0dd02bf56cec7d9f178 100644
--- a/pkg/analysis_server/test/package_uri_resolver_test.dart
+++ b/pkg/analysis_server/test/package_uri_resolver_test.dart
@@ -4,6 +4,8 @@
 
 library test.resolver.package;
 
+import 'dart:collection';
+
 import 'package:analysis_server/src/package_uri_resolver.dart';
 import 'package:analysis_server/src/resource.dart';
 import 'package:analyzer/src/generated/source.dart';
@@ -22,7 +24,7 @@ main() {
 
 @ReflectiveTestCase()
 class _PackageMapUriResolverTest {
-  static const EMPTY_MAP = const <String, List<Folder>>{};
+  static HashMap EMPTY_MAP = new HashMap<String, List<Folder>>();
   MemoryResourceProvider provider = new MemoryResourceProvider();
 
   setUp() {