Analyze locals in await for loops as inside a try-finally.

pkg/compiler/lib/src/closure.dart

Index: pkg/compiler/lib/src/closure.dart
diff --git a/pkg/compiler/lib/src/closure.dart b/pkg/compiler/lib/src/closure.dart
index fbefe05b7dd83c3f74655b77bef969d9c1c558d7..29588b88a6b8d1b74777d381c82f8369286c31df 100644
--- a/pkg/compiler/lib/src/closure.dart
+++ b/pkg/compiler/lib/src/closure.dart
@@ -1028,6 +1028,18 @@ class ClosureTranslator extends Visitor {
     node.visitChildren(this);
     inTryStatement = oldInTryStatement;
   }
+
+  visitForIn(ForIn node) {
+    if (node.awaitToken != null) {
+      // An `await for` loop is enclosed in an implicit try-finally.
+      bool oldInTryStatement = inTryStatement;
+      inTryStatement = true;
+      node.visitChildren(this);
+      inTryStatement = oldInTryStatement;
+    } else {
+      node.visitChildren(this);
+    }
+  }
 }
 
 /// A type variable as a local variable.