Complain about assignments to parenthesized expressions.

pkg/front_end/tool/fasta_perf.dart

 // Copyright (c) 2017, 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.
 
 /// An entrypoint used to run portions of fasta and measure its performance.
 library front_end.tool.fasta_perf;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:analyzer/src/fasta/ast_builder.dart';
 import 'package:front_end/src/fasta/dill/dill_target.dart' show DillTarget;
 import 'package:front_end/src/fasta/kernel/kernel_target.dart'
     show KernelTarget;
 import 'package:front_end/src/fasta/parser.dart';
 import 'package:front_end/src/fasta/scanner.dart';
 import 'package:front_end/src/fasta/scanner/io.dart' show readBytesFromFileSync;
-import 'package:front_end/src/fasta/scanner/precedence.dart';
 import 'package:front_end/src/fasta/source/scope_listener.dart' show Scope;
 import 'package:front_end/src/fasta/ticker.dart' show Ticker;
 import 'package:front_end/src/fasta/translate_uri.dart' show TranslateUri;
 import 'package:front_end/src/fasta/translate_uri.dart';
 
 /// Cumulative total number of chars scanned.
 int inputSize = 0;
 
 /// Cumulative time spent scanning.
 Stopwatch scanTimer = new Stopwatch();
@@ skipping 259 matching lines @@
 /// Report that metric [name] took [time] micro-seconds to process
 /// [inputSize] characters.
 void report(String name, int time) {
   var sb = new StringBuffer();
   var padding = ' ' * (20 - name.length);
   sb.write('$name:$padding $time us, ${time ~/ 1000} ms');
   var invSpeed = (time * 1000 / inputSize).toStringAsFixed(2);
   sb.write(', $invSpeed ns/char');
   print('$sb');
 }