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 c67afb43fafc5ca3fafa673473625c65c1d21280..8fce7ab420726ebb5493e44b764f96b09406cc6e 100644
--- a/pkg/compiler/lib/src/ssa/builder.dart
+++ b/pkg/compiler/lib/src/ssa/builder.dart
@@ -29,8 +29,8 @@ class SsaFunctionCompiler implements FunctionCompiler {
         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 +51,7 @@ 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(