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

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

Index: pkg/analyzer/lib/src/dart/ast/ast.dart
diff --git a/pkg/analyzer/lib/src/dart/ast/ast.dart b/pkg/analyzer/lib/src/dart/ast/ast.dart
index 2825ef56b73733f1ccd3369cfdee168878951e51..08f5056a1b0188b5ae27a270251748c533bc9a49 100644
--- a/pkg/analyzer/lib/src/dart/ast/ast.dart
+++ b/pkg/analyzer/lib/src/dart/ast/ast.dart
@@ -4063,6 +4063,9 @@ abstract class ExpressionImpl extends AstNodeImpl implements Expression {
     }
     return null;
   }
+
+  @override
+  Expression get unParenthesized => this;
 }
 
 /**
@@ -7915,6 +7918,17 @@ class ParenthesizedExpressionImpl extends ExpressionImpl
   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);