Address review comments from CL 10151014.

dart/lib/compiler/implementation/dart2js.dart

 // Copyright (c) 2012, 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('dart2js');
 
 #import('dart:io');
 #import('dart:uri');
 #import('dart:utf');
 
@@ skipping 22 matching lines @@
       verbose = true;
     } else if (argument.startsWith('--library-root=')) {
       String path =
           nativeToUriPath(argument.substring(argument.indexOf('=') + 1));
       if (!path.endsWith("/")) path = "$path/";
       libraryRoot = cwd.resolve(path);
     } else if (argument.startsWith('--out=')) {
       String path =
           nativeToUriPath(argument.substring(argument.indexOf('=') + 1));
       out = cwd.resolve(path);
-    } else if (argument == '--allow-mock-compilation') {
+    } else if ('--allow-mock-compilation' == argument) {
       options.add(argument);
     } else if (argument.startsWith('-')) {
       fail('Unknown option $argument.');
     } else {
       arguments.add(nativeToUriPath(argument));
     }
   }
   if (arguments.isEmpty()) {
-    fail('No files to compile.');
+    fail('No file to compile.');
   }
   if (arguments.length > 1) {
     var extra = arguments.getRange(1, arguments.length - 1);
     fail('Extra arguments: $extra.');
   }
 
   Map<String, SourceFile> sourceFiles = <SourceFile>{};
   int dartBytesRead = 0;
 
   Future<String> provider(Uri uri) {
@@ skipping 64 matching lines @@
   var buffer = new List<int>(length);
   var bytes = file.readListSync(buffer, 0, length);
   file.closeSync();
   return new String.fromCharCodes(new Utf8Decoder(buffer).decodeRest());
 }
 
 void fail(String message) {
   print(message);
   exit(1);
 }