First pass at asynchronous input loading in dart2js.

sdk/lib/_internal/compiler/compiler.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 compiler;
 
 import 'dart:async';
 import 'implementation/apiimpl.dart';
 
 // Unless explicitly allowed, passing [:null:] for any argument to the
@@ skipping 74 matching lines @@
     throw new ArgumentError("packageRoot must end with a /");
   }
   // TODO(ahe): Consider completing the future with an exception if
   // code is null.
   Compiler compiler = new Compiler(inputProvider,
                                    outputProvider,
                                    handler,
                                    libraryRoot,
                                    packageRoot,
                                    options);
-  compiler.run(script);
-  String code = compiler.assembledCode;
-  if (code != null && outputProvider != null) {
-    String outputType = 'js';
-    if (options.contains('--output-type=dart')) {
-      outputType = 'dart';
+  // TODO(ahe): Use the value of the future (which signals success or failure).
+  return compiler.run(script).then((_) {
+    String code = compiler.assembledCode;
+    if (code != null && outputProvider != null) {
+      String outputType = 'js';
+      if (options.contains('--output-type=dart')) {
+        outputType = 'dart';
+      }
+      outputProvider('', outputType)
+          ..add(code)
+          ..close();
+      code = ''; // Non-null signals success.
     }
-    outputProvider('', outputType)
-        ..add(code)
-        ..close();
-    code = ''; // Non-null signals success.
-  }
-  return new Future.value(code);
+    return code;
+  });
 }
 
 /**
  * Kind of diagnostics that the compiler can report.
  */
 class Diagnostic {
   /**
    * An error as identified by the "Dart Programming Language
    * Specification" [http://www.dartlang.org/docs/spec/].
    *
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   final String name;
 
   /**
    * This constructor is not private to support user-defined
    * diagnostic kinds.
    */
   const Diagnostic(this.ordinal, this.name);
 
   String toString() => name;
 }