Change the behavior of open on files to not truncate by default

tests/standalone/src/FileInvalidArgumentsTest.dart

 // Copyright (c) 2011, 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.
 
 class FileTest {
   static void testOpenInvalidArgs(name, [writable = false]) {
     var file = new File(name);
     try {
       file.openSync();
       Expect.fail('exception expected');
@@ skipping 70 matching lines @@
     };
     file.readList(buffer, offset, length);
     file.closeHandler = () {
       Expect.equals(1, errors);
     };
     file.close();
   }
 
   static void testWriteByteInvalidArgs(value) {
     String filename = getFilename("tests/vm/data/fixed_length_file");
-    var file = (new File(filename + "_out")).openSync(true);
+    var file = (new File(filename + "_out")).openSync(FileMode.WRITE);
     try {
       file.writeByteSync(value);
       Expect.fail('exception expected');
     } catch (var e) {
       Expect.isTrue(e is FileIOException);
       Expect.isTrue(e.toString().contains('Invalid argument'));
     }
 
     var errors = 0;
     file.errorHandler = (s) {
       errors++;
       Expect.isTrue(s.contains('Invalid argument'));
     };
     file.noPendingWriteHandler = (bytes) {
       Expect.fail('write list invalid argument');
     };
     file.writeByte(value);
     file.closeHandler = () {
       Expect.equals(1, errors);
     };
     file.close();
   }
 
   static void testWriteListInvalidArgs(buffer, offset, bytes) {
     String filename = getFilename("tests/vm/data/fixed_length_file");
-    var file = (new File(filename + "_out")).openSync(true);
+    var file = (new File(filename + "_out")).openSync(FileMode.WRITE);
     try {
       file.writeListSync(buffer, offset, bytes);
       Expect.fail('exception expected');
     } catch (var e) {
       Expect.isTrue(e is FileIOException);
       Expect.isTrue(e.toString().contains('Invalid arguments'));
     }
 
     var errors = 0;
     file.errorHandler = (s) {
       errors++;
       Expect.isTrue(s.contains('Invalid arguments'));
     };
     file.noPendingWriteHandler = (bytes) {
       Expect.fail('write list invalid argument');
     };
     file.writeList(buffer, offset, bytes);
     file.closeHandler = () {
       Expect.equals(1, errors);
     };
     file.close();
   }
 
   static void testWriteStringInvalidArgs(string) {
     String filename = getFilename("tests/vm/data/fixed_length_file");
     var file = new File(filename + "_out");
-    file.openSync(true);
+    file.openSync(FileMode.WRITE);
     try {
       file.writeString(string);
       Expect.fail('exception expected');
     } catch (var e) {
       Expect.isTrue(e is FileIOException);
       Expect.isTrue(e.toString().contains('writeString failed'));
     }
 
     var errors = 0;
     file.errorHandler = (s) {
@@ skipping 40 matching lines @@
   FileTest.testCreateInvalidArgs(0);
   FileTest.testReadListInvalidArgs(12, 0, 1);
   FileTest.testReadListInvalidArgs(new List(10), '0', 1);
   FileTest.testReadListInvalidArgs(new List(10), 0, '1');
   FileTest.testWriteByteInvalidArgs('asdf');
   FileTest.testWriteListInvalidArgs(12, 0, 1);
   FileTest.testWriteListInvalidArgs(new List(10), '0', 1);
   FileTest.testWriteListInvalidArgs(new List(10), 0, '1');
   FileTest.testFullPathInvalidArgs(12);
 }