Add a (public) utility method to clean-up code

pkg/analyzer/lib/src/dart/ast/ast.dart

 // Copyright (c) 2014, 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.
 
 library analyzer.src.dart.ast.ast;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 4045 matching lines @@
       if (identical(parent.rightHandSide, this)) {
         return parent._staticParameterElementForRightHandSide;
       }
     } else if (parent is PrefixExpressionImpl) {
       return parent._staticParameterElementForOperand;
     } else if (parent is PostfixExpressionImpl) {
       return parent._staticParameterElementForOperand;
     }
     return null;
   }
+
+  @override
+  Expression get unParenthesized => this;
 }
 
 /**
  * An expression used as a statement.
  *
  *    expressionStatement ::=
  *        [Expression]? ';'
  */
 class ExpressionStatementImpl extends StatementImpl
     implements ExpressionStatement {
@@ skipping 3832 matching lines @@
 
   @override
   void set expression(Expression expression) {
     _expression = _becomeParentOf(expression);
   }
 
   @override
   int get precedence => 15;
 
   @override
+  Expression get unParenthesized {
+    // This is somewhat inefficient, but it avoids a stack overflow in the
+    // degenerate case.
+    Expression expression = _expression;
+    while (expression is ParenthesizedExpressionImpl) {
+      expression = (expression as ParenthesizedExpressionImpl)._expression;
+    }
+    return expression;
+  }
+
+  @override
   dynamic/*=E*/ accept/*<E>*/(AstVisitor/*<E>*/ visitor) =>
       visitor.visitParenthesizedExpression(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     _expression?.accept(visitor);
   }
 }
 
 /**
@@ skipping 3051 matching lines @@
 
   @override
   dynamic/*=E*/ accept/*<E>*/(AstVisitor/*<E>*/ visitor) =>
       visitor.visitYieldStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     _expression?.accept(visitor);
   }
 }