fixes #28032, await in cascade

pkg/dev_compiler/lib/src/compiler/js_metalet.dart

Index: pkg/dev_compiler/lib/src/compiler/js_metalet.dart
diff --git a/pkg/dev_compiler/lib/src/compiler/js_metalet.dart b/pkg/dev_compiler/lib/src/compiler/js_metalet.dart
index 8e341fe5e341d6602dfd73da10405117002a7bb3..3645dc1e9b6d0b0579d0485b05bc3dc18235c6cc 100644
--- a/pkg/dev_compiler/lib/src/compiler/js_metalet.dart
+++ b/pkg/dev_compiler/lib/src/compiler/js_metalet.dart
@@ -333,6 +333,7 @@ class _YieldFinder extends BaseVisitor {
   bool hasYield = false;
   bool hasThis = false;
   bool _nestedFunction = false;
+
   @override
   visitThis(This node) {
     hasThis = true;
@@ -353,6 +354,7 @@ class _YieldFinder extends BaseVisitor {
 
   @override
   visitNode(Node node) {
-    if (!hasYield) super.visitNode(node);

[Jennifer Messerly, 2016/12/07 21:57:20]

DOH!

+    if (hasYield && hasThis) return; // found both, nothing more to do.
+    super.visitNode(node);
   }
 }