Fix 56 hints in pkg/compiler

pkg/compiler/lib/src/source_file_provider.dart

 // Copyright (c) 2013, 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 source_file_provider;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 import 'dart:math' as math;
 
 import '../compiler.dart' as api show Diagnostic, DiagnosticHandler;
 import 'dart2js.dart' show AbortLeg;
 import 'colors.dart' as colors;
 import 'io/source_file.dart';
 import 'filenames.dart';
 import 'util/uri_extras.dart';
 import 'dart:typed_data';
 
 List<int> readAll(String filename) {
   var file = (new File(filename)).openSync();
   var length = file.lengthSync();
   // +1 to have a 0 terminated list, see [Scanner].
   var buffer = new Uint8List(length + 1);
-  var bytes = file.readIntoSync(buffer, 0, length);
+  file.readIntoSync(buffer, 0, length);
   file.closeSync();
   return buffer;
 }
 
 abstract class SourceFileProvider {
   bool isWindows = (Platform.operatingSystem == 'windows');
   Uri cwd = currentDirectory;
   Map<Uri, SourceFile> sourceFiles = <Uri, SourceFile>{};
   int dartCharactersRead = 0;
 
@@ skipping 289 matching lines @@
   var onAdd, onClose;
 
   EventSinkWrapper(this.onAdd, this.onClose);
 
   void add(String data) => onAdd(data);
 
   void addError(error, [StackTrace stackTrace]) => throw error;
 
   void close() => onClose();
 }