dart2js: add --preserve-uris flag.

sdk/lib/_internal/compiler/js_lib/js_mirrors.dart

Index: sdk/lib/_internal/compiler/js_lib/js_mirrors.dart
diff --git a/sdk/lib/_internal/compiler/js_lib/js_mirrors.dart b/sdk/lib/_internal/compiler/js_lib/js_mirrors.dart
index af3226e9391822a9d3eb0892585874171ebcd583..5f613d37079abbf891ba64dff62a97645616f613 100644
--- a/sdk/lib/_internal/compiler/js_lib/js_mirrors.dart
+++ b/sdk/lib/_internal/compiler/js_lib/js_mirrors.dart
@@ -141,7 +141,17 @@ class JsMirrorSystem implements MirrorSystem {
     if (jsLibraries == null) return result;
     for (List data in jsLibraries) {
       String name = data[0];
-      Uri uri = Uri.parse(data[1]);
+      String uriString = data[1];
+      Uri uri;
+      // The Uri has been compiled out. Create a URI from the simple name.
+      if (uriString != "") {
+        uri = Uri.parse(uriString);
+      } else {
+        uri = new Uri(scheme: 'https',
+                      host: 'dartlang.org',
+                      path: 'dart2js-stripped-uri',
+                      queryParameters: { 'lib': name });
+      }
       List<String> classes = data[2];
       List<String> functions = data[3];
       var metadataFunction = data[4];