Change "FormatException.position" to be named "offset".

tests/corelib/format_exception_test.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.
 
 library format_exception_test;
 import "package:expect/expect.dart";
 
-test(exn, message, source, position, toString) {
+test(exn, message, source, offset, toString) {
   Expect.equals(message, exn.message);
   Expect.equals(source, exn.source);
-  Expect.equals(position, exn.position);
+  Expect.equals(offset, exn.offset);
   Expect.equals(toString, exn.toString());
 }
 
 main() {
   var e;
   e = new FormatException();
   test(e, "", null, null, "FormatException");
   e = new FormatException("");
   test(e, "", null, null, "FormatException");
   e = new FormatException(null);
@@ skipping 10 matching lines @@
                                           "source" * 12 + "sou...");
   e = new FormatException("message", "source" * 25);
   test(e, "message", "source" * 25, null, "FormatException: message\n" +
                                           "source" * 12 + "sou...");
   e = new FormatException("message", "s1\nsource\ns2");
   test(e, "message", "s1\nsource\ns2", null, "FormatException: message\n" +
                                              "s1\nsource\ns2");
 
   var o = new Object();
   e = new FormatException("message", o, 10);
-  test(e, "message", o, 10, "FormatException: message (at position 10)");
+  test(e, "message", o, 10, "FormatException: message (at offset 10)");
 
   e = new FormatException("message", "source", 3);
   test(e, "message", "source", 3,
        "FormatException: message (at character 4)\nsource\n   ^\n");
 
   e = new FormatException("message", "s1\nsource\ns2", 6);
   test(e, "message", "s1\nsource\ns2", 6,
        "FormatException: message (at line 2, character 4)\nsource\n   ^\n");
 
   var longline = "watermelon cantaloupe " * 8 + "watermelon";  // Length > 160.
@@ skipping 11 matching lines @@
        "...${longline.substring(longline.length - 75)}\n"
        "${' ' * 78}^\n");
 
   var half = longline.length ~/ 2;
   e = new FormatException("message", longsource, line10 + half);
   test(e, "message", longsource, line10 + half,
        "FormatException: message (at line 10, character ${half + 1})\n"
        "...${longline.substring(half - 36, half + 36)}...\n"
        "${' ' * 39}^\n");
 }