Support root-relative paths on Windows.

Support root-relative paths on Windows.

On Windows, a leading slash in a path means that that path should be
relative to the current drive. So for example, `join(r"C:\foo",
r"\bar")` should return "C:\bar".

R=rnystrom@google.com
BUG=14918
Committed: https://code.google.com/p/dart/source/detail?r=30295

[Bob Nystrom, 2013-11-14 17:05:08]

https://codereview.chromium.org/68503011/diff/1/pkg/path/lib/path.dart
File pkg/path/lib/path.dart (right):

https://codereview.chromium.org/68503011/diff/1/pkg/path/lib/path.dart#newcod...
pkg/path/lib/path.dart:569: buffer.write(parsed.toString());
The toString() isn't needed here.

https://codereview.chromium.org/68503011/diff/1/pkg/path/lib/path.dart#newcod...
pkg/path/lib/path.dart:988: final relativeRootPattern = new
RegExp(r"^[/\\](?![/\\])");
Doc comment for this please. Regexen are opaque.

https://codereview.chromium.org/68503011/diff/1/pkg/path/test/windows_test.dart
File pkg/path/test/windows_test.dart (right):

https://codereview.chromium.org/68503011/diff/1/pkg/path/test/windows_test.da...
pkg/path/test/windows_test.dart:222: expect(builder.join('a', r'\b'), r'\b');
These are really part of the next test now. Either move them down or ditch them
if they're redundant with tests below.

https://codereview.chromium.org/68503011/diff/1/pkg/path/test/windows_test.da...
pkg/path/test/windows_test.dart:271: expect(builder.joinAll(['a', r'\b']),
r'\b');
Ditto.

https://codereview.chromium.org/68503011/diff/1/pkg/path/test/windows_test.da...
pkg/path/test/windows_test.dart:472: // expect(r.relative(r'C:\a\b'),
equals(r'C:\a\b'));
Why are these commented out?

[nweiz, 2013-11-14 21:10:16]

https://codereview.chromium.org/68503011/diff/1/pkg/path/lib/path.dart
File pkg/path/lib/path.dart (right):

https://codereview.chromium.org/68503011/diff/1/pkg/path/lib/path.dart#newcod...
pkg/path/lib/path.dart:569: buffer.write(parsed.toString());
On 2013/11/14 17:05:08, Bob Nystrom wrote:
> The toString() isn't needed here.

Done.

https://codereview.chromium.org/68503011/diff/1/pkg/path/lib/path.dart#newcod...
pkg/path/lib/path.dart:988: final relativeRootPattern = new
RegExp(r"^[/\\](?![/\\])");
On 2013/11/14 17:05:08, Bob Nystrom wrote:
> Doc comment for this please. Regexen are opaque.

Done.

https://codereview.chromium.org/68503011/diff/1/pkg/path/test/windows_test.dart
File pkg/path/test/windows_test.dart (right):

https://codereview.chromium.org/68503011/diff/1/pkg/path/test/windows_test.da...
pkg/path/test/windows_test.dart:222: expect(builder.join('a', r'\b'), r'\b');
On 2013/11/14 17:05:08, Bob Nystrom wrote:
> These are really part of the next test now. Either move them down or ditch
them
> if they're redundant with tests below.

Done.

https://codereview.chromium.org/68503011/diff/1/pkg/path/test/windows_test.da...
pkg/path/test/windows_test.dart:271: expect(builder.joinAll(['a', r'\b']),
r'\b');
On 2013/11/14 17:05:08, Bob Nystrom wrote:
> Ditto.

Done.

https://codereview.chromium.org/68503011/diff/1/pkg/path/test/windows_test.da...
pkg/path/test/windows_test.dart:472: // expect(r.relative(r'C:\a\b'),
equals(r'C:\a\b'));
On 2013/11/14 17:05:08, Bob Nystrom wrote:
> Why are these commented out?

Leftover from debugging. Uncommented.

[Bob Nystrom, 2013-11-14 22:43:41]

LGTM!

[nweiz, 2013-11-14 22:50:51]

Committed patchset #2 manually as r30295 (presubmit successful).