First pass at asynchronous input loading in dart2js.

sdk/lib/_internal/compiler/samples/leap/leap_leg.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.
 
 compilerIsolate(port) {
   Runner runner = new Runner();
   runner.init();
 
   port.receive((msg, replyTo) {
     replyTo.send(runner.update(msg));
@@ skipping 107 matching lines @@
   });
 }
 
 class Runner {
   final LeapCompiler compiler;
 
   Runner() : compiler = new LeapCompiler();
 
   String init() {
     Stopwatch sw = new Stopwatch()..start();
+    // TODO(rnystrom): This is broken now that scanBuiltInLibraries is async.
+    // Delete this sample.
     compiler.scanBuiltinLibraries();
     sw.stop();
     return 'Scanned core libraries in ${sw.elapsedMilliseconds}ms';
   }
 
   String update(String codeText) {
     StringBuffer sb = new StringBuffer();
 
     Stopwatch sw = new Stopwatch()..start();
 
@@ skipping 76 matching lines @@
   final libDir = "../..";
 
   LeapCompiler() : cache = new HttpRequestCache(), super() {
     tasks = [scanner, dietParser, parser, resolver, checker];
   }
 
   void log(message) { print(message); }
 
   String get legDirectory => libDir;
 
+  // TODO(rnystrom): This is broken now that scanBuiltInLibraries is async.
+  // Delete this sample.
   LibraryElement scanBuiltinLibrary(String path) {
     Uri base = Uri.parse(html.window.location.toString());
     Uri libraryRoot = base.resolve(libDir);
     Uri resolved = libraryRoot.resolve(DART2JS_LIBRARY_MAP[path]);
+    // TODO(rnystrom): This is broken now that scanBuiltInLibraries is async.
+    // Delete this sample.
     LibraryElement library = scanner.loadLibrary(resolved, null);
     return library;
   }
 
   currentScript() {
     if (currentElement == null) return null;
     CompilationUnitElement compilationUnit =
       currentElement.getCompilationUnit();
     if (compilationUnit == null) return null;
     return compilationUnit.script;
   }
 
+  // TODO(rnystrom): This is broken now that scanBuiltInLibraries is async.
+  // Delete this sample.
   Script readScript(Uri uri, [ScriptTag node]) {
     String text = "";
     try {
       text = cache.readAll(uri.path.toString());
     } catch (exception) {
       cancel("${uri.path}: $exception", node: node);
     }
     SourceFile sourceFile = new SourceFile(uri.toString(), text);
     return new Script(uri, sourceFile);
   }
@@ skipping 28 matching lines @@
     mainApp = new LibraryElement(script);
 
     universe.libraries.remove(script.uri.toString());
     Element element;
     withCurrentElement(mainApp, () {
         scanner.scan(mainApp);
       });
     return mainApp;
   }
 }