Implementation of async-await transformation on js ast.

pkg/compiler/lib/src/compiler.dart

Index: pkg/compiler/lib/src/compiler.dart
diff --git a/pkg/compiler/lib/src/compiler.dart b/pkg/compiler/lib/src/compiler.dart
index 9b3f9c920c7a69395e76e62a669473d6b70a014f..cffa2e0025c61be0cf4b07677a658e9b24207261 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -176,6 +176,11 @@ class CodegenRegistry extends Registry {
   void registerInstantiation(InterfaceType type) {
     world.registerInstantiatedType(type, this);
   }
+
+  void registerAsyncMarker(FunctionElement element) {
+    backend.registerAsyncMarker(element, world, this);
+  }
+
 }
 
 /// [WorkItem] used exclusively by the [CodegenEnqueuer].
@@ -229,6 +234,8 @@ abstract class Registry {
   void registerInstantiation(InterfaceType type);
 
   void registerGetOfStaticFunction(FunctionElement element);
+
+  void registerAsyncMarker(FunctionElement element);
 }
 
 abstract class Backend {
@@ -516,6 +523,10 @@ abstract class Backend {
   void forgetElement(Element element) {}
 
   void registerMainHasArguments(Enqueuer enqueuer) {}
+
+  void registerAsyncMarker(FunctionElement element,
+                             Enqueuer enqueuer,
+                             Registry registry) {}
 }
 
 /// Backend callbacks function specific to the resolution phase.
@@ -740,9 +751,6 @@ abstract class Compiler implements DiagnosticListener {
 
   final bool suppressWarnings;
 
-  /// `true` if async/await features are supported.
-  final bool enableAsyncAwait;
-
   /// If `true`, some values are cached for reuse in incremental compilation.
   /// Incremental compilation is basically calling [run] more than once.
   final bool hasIncrementalSupport;
@@ -1004,7 +1012,6 @@ abstract class Compiler implements DiagnosticListener {
             this.suppressWarnings: false,
             bool hasIncrementalSupport: false,
             this.enableExperimentalMirrors: false,
-            this.enableAsyncAwait: false,
             this.allowNativeExtensions: false,
             this.generateCodeWithCompileTimeErrors: false,
             api.CompilerOutputProvider outputProvider,