Reapply "Add support for timezone offset and timezone name."

Reapply "Add support for timezone offset and timezone name."

This reapplies commit 7800.
Original CL: https://chromiumcodereview.appspot.com/10383218/

Don't write *foo += x.

Committed: https://code.google.com/p/dart/source/detail?r=7803

[floitsch, 2012-05-21 14:49:39]

Forgot to upload before the fix.
The only line that changed was os_win.cc:100.

[floitsch, 2012-05-21 14:53:09]

There is still something else broken.
Will fix that right away and then inform you when the CL is ready again.

[floitsch, 2012-05-21 14:59:14]

Updated status file for frog.

[Mads Ager (google), 2012-05-21 15:02:55]

lgtm

https://chromiumcodereview.appspot.com/10413031/diff/2002/tests/corelib/corel...
File tests/corelib/corelib.status (right):

https://chromiumcodereview.appspot.com/10413031/diff/2002/tests/corelib/corel...
tests/corelib/corelib.status:37: date_time7_test: Skip  # New methods
(timeZoneName and timeZoneOffset) were not ported to frog.
Use two lines for the comment?

[floitsch, 2012-05-21 15:06:32]

https://chromiumcodereview.appspot.com/10413031/diff/2002/tests/corelib/corel...
File tests/corelib/corelib.status (right):

https://chromiumcodereview.appspot.com/10413031/diff/2002/tests/corelib/corel...
tests/corelib/corelib.status:37: date_time7_test: Skip  # New methods
(timeZoneName and timeZoneOffset) were not ported to frog.
On 2012/05/21 15:02:55, Mads Ager wrote:
> Use two lines for the comment?

Moved the comment before the Skip line.