Better hints for await in non-async functions

pkg/compiler/lib/src/typechecker.dart

Index: pkg/compiler/lib/src/typechecker.dart
diff --git a/pkg/compiler/lib/src/typechecker.dart b/pkg/compiler/lib/src/typechecker.dart
index c126bd237deba192ee612929b857b15d0eba502e..781301c6427dcec6940fc62acc185b8ca81f929a 100644
--- a/pkg/compiler/lib/src/typechecker.dart
+++ b/pkg/compiler/lib/src/typechecker.dart
@@ -817,6 +817,14 @@ class TypeCheckerVisitor extends Visitor<DartType> {
               // getter.
               reportTypeWarning(node, MessageKind.GETTER_NOT_FOUND,
                   {'className': receiverType.name, 'memberName': name});
+            } else if (name == 'await') {
+              var enclosingFunctionName = executableContext.name;
+              reportTypeWarning(node, MessageKind.AWAIT_MEMBER_NOT_FOUND,
+                  {'className': receiverType.name,
+                   'enclosingFunctionText': enclosingFunctionName == ''
+                       ? 'the enclosing function'
+                       : "'$enclosingFunctionName'"
+                  });
             } else {
               reportTypeWarning(node, MessageKind.MEMBER_NOT_FOUND,
                   {'className': receiverType.name, 'memberName': name});