Ensure that parser throws an error when parsing x is! T with malformed type T.

runtime/vm/parser.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/parser.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/compiler_stats.h"
@@ skipping 6566 matching lines @@
         }
         const intptr_t type_pos = TokenPos();
         const AbstractType& type =
             AbstractType::ZoneHandle(ParseType(ClassFinalizer::kCanonicalize));
         if (!type.IsInstantiated() &&
             (current_block_->scope->function_level() > 0)) {
           // Make sure that the instantiator is captured.
           CaptureInstantiator();
         }
         right_operand = new TypeNode(type_pos, type);
-        if ((op_kind == Token::kIS) && type.IsMalformed()) {
+        if (((op_kind == Token::kIS) || (op_kind == Token::kISNOT)) &&
+            type.IsMalformed()) {
           // Note that a type error is thrown even if the tested value is null
           // in a type test. However, no cast exception is thrown if the value
           // is null in a type cast.
           return ThrowTypeError(type_pos, type);
         }
       }
       if (Token::IsRelationalOperator(op_kind)
           || Token::IsTypeTestOperator(op_kind)
           || Token::IsTypeCastOperator(op_kind)
           || Token::IsEqualityOperator(op_kind)) {
@@ skipping 2911 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart