[kernel] Fix assert message.

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 3143 matching lines @@
   accept(StatementVisitor v) => v.visitEmptyStatement(this);
   accept1(StatementVisitor1 v, arg) => v.visitEmptyStatement(this, arg);
 
   visitChildren(Visitor v) {}
   transformChildren(Transformer v) {}
 }
 
 class AssertStatement extends Statement {
   Expression condition;
   Expression message; // May be null.
+  int conditionStartOffset;
+  int conditionEndOffset;
 
-  AssertStatement(this.condition, [this.message]) {
+  AssertStatement(this.condition,
+      {this.message, this.conditionStartOffset, this.conditionEndOffset}) {
     condition?.parent = this;
     message?.parent = this;
   }
 
   accept(StatementVisitor v) => v.visitAssertStatement(this);
   accept1(StatementVisitor1 v, arg) => v.visitAssertStatement(this, arg);
 
   visitChildren(Visitor v) {
     condition?.accept(v);
     message?.accept(v);
@@ skipping 1437 matching lines @@
 /// typedef has not been assigned a canonical name yet.
 ///
 /// Returns `null` if the typedef is `null`.
 CanonicalName getCanonicalNameOfTypedef(Typedef typedef_) {
   if (typedef_ == null) return null;
   if (typedef_.canonicalName == null) {
     throw '$typedef_ has no canonical name';
   }
   return typedef_.canonicalName;
 }