Perform incremental compilation, and run the updated program.

dart/pkg/dart2js_incremental/lib/library_updater.dart

 // Copyright (c) 2014, 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 dart2js_incremental.library_updater;
 
 import 'dart:async' show
     Future;
 
 import 'dart:convert' show
@@ skipping 67 matching lines @@
 
   /// Used as tear-off passed to [LibraryLoaderTask.resetAsync].
   Future<bool> reuseLibrary(LibraryElement library) {
     assert(compiler != null);
     if (library.isPlatformLibrary || library.isPackageLibrary) {
       logTime('Reusing $library.');
       return new Future.value(true);
     } else if (library != compiler.mainApp) {
       return new Future.value(false);
     }
-    return inputProvider(uri).then((List<int> bytes) {
+    return inputProvider(uri).then((bytes) {
       return canReuseLibrary(library, bytes);
     });
   }
 
   /// Returns true if [library] can be reused.
   ///
   /// This methods also computes the [updates] (patches) needed to have
   /// [library] reflect the modifications in [bytes].
-  bool canReuseLibrary(LibraryElement library, List<int> bytes) {
+  bool canReuseLibrary(LibraryElement library, bytes) {
     logTime('Attempting to reuse mainApp.');
-    String newSource = UTF8.decode(bytes);
+    String newSource = bytes is String ? bytes : UTF8.decode(bytes);
     logTime('Decoded UTF8');
 
     // TODO(ahe): Can't use compiler.mainApp in general.
     if (false && newSource == compiler.mainApp.compilationUnit.script.text) {
       // TODO(ahe): Need to update the compilationUnit's source code when
       // doing incremental analysis for this to work.
       logTime("Source didn't change");
       return true;
     }
 
@@ skipping 71 matching lines @@
     updates.add(new FunctionUpdate(compiler, before, after));
     return true;
   }
 
   List<Element> applyUpdates() {
     return updates.map((Update update) => update.apply()).toList();
   }
 
   String computeUpdateJs() {
     List<Element> updatedElements = applyUpdates();
-    compiler.progress.reset();
+    if (compiler.progress != null) {
+      compiler.progress.reset();
+    }
     for (Element element in updatedElements) {
       compiler.enqueuer.resolution.addToWorkList(element);
     }
     compiler.processQueue(compiler.enqueuer.resolution, null);
 
     compiler.phase = Compiler.PHASE_DONE_RESOLVING;
 
     for (Element element in updatedElements) {
       compiler.enqueuer.codegen.addToWorkList(element);
     }
@@ skipping 79 matching lines @@
     before.getOrSet = after.getOrSet;
   }
 
   /// Reset various caches and remove this element from the compiler's internal
   /// state.
   void reuseElement() {
     compiler.forgetElement(before);
     before.reuseElement();
   }
 }