Add Duration.inMicroseconds and add Stopwatch.elapsed.

Add Duration.inMicroseconds and add Stopwatch.elapsed.

Committed: https://code.google.com/p/dart/source/detail?r=19406

[floitsch, 2013-03-01 18:10:12]

Note: this CL also makes Duration non-implementable (since it has a private
member now).

[Lasse Reichstein Nielsen, 2013-03-04 09:11:05]

lgtm

https://codereview.chromium.org/12389056/diff/1/sdk/lib/core/duration.dart
File sdk/lib/core/duration.dart (right):

https://codereview.chromium.org/12389056/diff/1/sdk/lib/core/duration.dart#ne...
sdk/lib/core/duration.dart:44: final int _duration;
Why not name it inMicroseconds instead, and not have a private member?

[floitsch, 2013-03-04 18:02:28]

https://codereview.chromium.org/12389056/diff/1/sdk/lib/core/duration.dart
File sdk/lib/core/duration.dart (right):

https://codereview.chromium.org/12389056/diff/1/sdk/lib/core/duration.dart#ne...
sdk/lib/core/duration.dart:44: final int _duration;
On 2013/03/04 09:11:05, Lasse Reichstein Nielsen wrote:
> Why not name it inMicroseconds instead, and not have a private member?

I prefer to be explicit when a class has an interface that is implementable.
If you feel strongly I can change it.

[floitsch, 2013-03-04 18:13:53]

Committed patchset #1 manually as r19406 (presubmit successful).