Add support for analyzing individual URIs.

pkg/compiler/lib/src/apiimpl.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library leg_apiimpl;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:package_config/packages.dart';
@@ skipping 364 matching lines @@
         notFound: (Uri notFound) {
           reportError(
               node,
               MessageKind.LIBRARY_NOT_FOUND,
               {'resolvedUri': uri}
           );
           return null;
         });
   }
 
+  Future<elements.LibraryElement> analyzeUri(
+      Uri uri,
+      {bool skipLibraryWithPartOfTag: true}) {
+    if (packages == null) {
+      return setupPackages(uri).then((_) => super.analyzeUri(uri));
+    }
+    return super.analyzeUri(
+        uri, skipLibraryWithPartOfTag: skipLibraryWithPartOfTag);
+  }
+
   Future setupPackages(Uri uri) {
     if (packageRoot != null) {
       // Use "non-file" packages because the file version requires a [Directory]
       // and we can't depend on 'dart:io' classes.
       packages = new NonFilePackagesDirectoryPackages(packageRoot);
     } else if (packageConfig != null) {
       return callUserProvider(packageConfig).then((packageConfigContents) {
         if (packageConfigContents is String) {
           packageConfigContents = UTF8.encode(packageConfigContents);
         }
@@ skipping 107 matching lines @@
     print('$message: ${tryToString(exception)}');
     print(tryToString(stackTrace));
   }
 
   fromEnvironment(String name) => environment[name];
 
   LibraryInfo lookupLibraryInfo(String libraryName) {
     return library_info.LIBRARIES[libraryName];
   }
 }