Fix error handling in dart2js async-await

pkg/compiler/lib/src/ssa/builder.dart

Index: pkg/compiler/lib/src/ssa/builder.dart
diff --git a/pkg/compiler/lib/src/ssa/builder.dart b/pkg/compiler/lib/src/ssa/builder.dart
index 404ac8d0ee7e51974e1109818e29c17abc66ff63..05e70e3b958c2fb7b4b75a96cb3ffccba72ad39a 100644
--- a/pkg/compiler/lib/src/ssa/builder.dart
+++ b/pkg/compiler/lib/src/ssa/builder.dart
@@ -25,12 +25,13 @@ class SsaFunctionCompiler implements FunctionCompiler {
       JavaScriptBackend backend = builder.backend;
 
       AsyncRewriter rewriter = null;
+
       if (element.asyncMarker == AsyncMarker.ASYNC) {
         rewriter = new AsyncRewriter(
             backend.compiler,
             backend.compiler.currentElement,
-            thenHelper:
-                backend.emitter.staticFunctionAccess(backend.getThenHelper()),
+            asyncHelper:
+                backend.emitter.staticFunctionAccess(backend.getAsyncHelper()),
             newCompleter: backend.emitter.staticFunctionAccess(
                 backend.getCompleterConstructor()),
             safeVariableName: backend.namer.safeVariableName);
@@ -51,7 +52,7 @@ class SsaFunctionCompiler implements FunctionCompiler {
             backend.compiler,
             backend.compiler.currentElement,
             streamHelper: backend.emitter.staticFunctionAccess(
-                backend.getStreamHelper()),
+                backend.getAsyncStarHelper()),
             streamOfController: backend.emitter.staticFunctionAccess(
                 backend.getStreamOfController()),
             newController: backend.emitter.staticFunctionAccess(