Add LibraryLoader.resetAsync.

dart/pkg/dart2js_incremental/lib/caching_compiler.dart

Index: dart/pkg/dart2js_incremental/lib/caching_compiler.dart
diff --git a/dart/pkg/dart2js_incremental/lib/caching_compiler.dart b/dart/pkg/dart2js_incremental/lib/caching_compiler.dart
index afdf92f8ffd7beda7b2ee167f9366fd4c82349a5..9adf0b96e1d37b8e4fbc62d6f32c950ece293cd4 100644
--- a/dart/pkg/dart2js_incremental/lib/caching_compiler.dart
+++ b/dart/pkg/dart2js_incremental/lib/caching_compiler.dart
@@ -6,7 +6,7 @@ part of dart2js_incremental;
 
 /// Do not call this method directly. It will be made private.
 // TODO(ahe): Make this method private.
-Compiler reuseCompiler(
+Future<Compiler> reuseCompiler(
     {DiagnosticHandler diagnosticHandler,
      CompilerInputProvider inputProvider,
      CompilerOutputProvider outputProvider,
@@ -16,7 +16,7 @@ Compiler reuseCompiler(
      Uri packageRoot,
      bool packagesAreImmutable: false,
      Map<String, dynamic> environment,
-     bool reuseLibrary(LibraryElement library)}) {
+     Future<bool> reuseLibrary(LibraryElement library)}) {
   UserTag oldTag = new UserTag('_reuseCompiler').makeCurrent();
   if (libraryRoot == null) {
     throw 'Missing libraryRoot';
@@ -55,14 +55,16 @@ Compiler reuseCompiler(
         print('Unable to reuse compiler.');
       }
     }
-    compiler = new Compiler(
-        inputProvider,
-        outputProvider,
-        diagnosticHandler,
-        libraryRoot,
-        packageRoot,
-        options,
-        environment);
+    oldTag.makeCurrent();
+    return new Future.value(
+        new Compiler(
+            inputProvider,
+            outputProvider,
+            diagnosticHandler,
+            libraryRoot,
+            packageRoot,
+            options,
+            environment));
   } else {
     for (final task in compiler.tasks) {
       if (task.watch != null) {
@@ -138,13 +140,14 @@ Compiler reuseCompiler(
 
     if (reuseLibrary == null) {
       reuseLibrary = (LibraryElement library) {
-        return
+        return new Future.value(
             library.isPlatformLibrary ||
-            (packagesAreImmutable && library.isPackageLibrary);
+            (packagesAreImmutable && library.isPackageLibrary));
       };
     }
-    compiler.libraryLoader.reset(reuseLibrary: reuseLibrary);
+    return compiler.libraryLoader.resetAsync(reuseLibrary).then((_) {
+      oldTag.makeCurrent();
+      return compiler;
+    });
   }
-  oldTag.makeCurrent();
-  return compiler;
 }