Add --verify-ir flag to dartk and test.py.

pkg/kernel/lib/ast.dart

 // Copyright (c) 2016, 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.
 
 /// -----------------------------------------------------------------------
 ///                           ERROR HANDLING
 /// -----------------------------------------------------------------------
 ///
 /// As a rule of thumb, errors that can be detected statically are handled by
 /// the frontend, typically by translating the erroneous code into a 'throw' or
@@ skipping 2994 matching lines @@
       bool isConst: false,
       this.type: const DynamicType()}) {
     assert(type != null);
     initializer?.parent = this;
     this.isFinal = isFinal;
     this.isConst = isConst;
   }
 
   static const int FlagFinal = 1 << 0; // Must match serialized bit positions.
   static const int FlagConst = 1 << 1;
+  static const int FlagInScope = 1 << 2; // Temporary flag used by verifier.
 
   bool get isFinal => flags & FlagFinal != 0;
   bool get isConst => flags & FlagConst != 0;
 
   void set isFinal(bool value) {
     flags = value ? (flags | FlagFinal) : (flags & ~FlagFinal);
   }
 
   void set isConst(bool value) {
     flags = value ? (flags | FlagConst) : (flags & ~FlagConst);
@@ skipping 606 matching lines @@
 
   @override
   defaultTreeNode(TreeNode node) {
     if (node == child) {
       return replacement;
     } else {
       return node;
     }
   }
 }