Optimize absolute() and normalize().

Optimize absolute() and normalize().

This short-circuits absolute() if the path is already absolute.
Detecting absolute paths is very fast, whereas join() is relatively
slow.

For normalize(), this runs a single-pass check over a path to see
whether it needs to be normalized at all. This check isn't free, but
it's a lot less costly than parsing and reserializing the path, and it
covers the common case.

See dart-lang/glob#24962

R=rnystrom@google.com

Committed: https://github.com/dart-lang/path/commit/9bad3dea80a64143e0354b4d06ce535b3945d801

[Bob Nystrom, 2015-11-17 23:55:10]

One suggestion then LGTM!

https://codereview.chromium.org/1455003002/diff/1/lib/src/context.dart
File lib/src/context.dart (right):

https://codereview.chromium.org/1455003002/diff/1/lib/src/context.dart#newcode82
lib/src/context.dart:82: if (isAbsolute(part1) && !isRootRelative(part1) &&
part2 == null) {
I'd move the null check first since that will be the fastest.

[nweiz, 2015-11-18 00:03:52]

Code review changes

[nweiz, 2015-11-18 00:04:01]

Committed patchset #2 (id:20001) manually as
9bad3dea80a64143e0354b4d06ce535b3945d801 (presubmit successful).

[nweiz, 2015-11-18 00:04:14]

https://codereview.chromium.org/1455003002/diff/1/lib/src/context.dart
File lib/src/context.dart (right):

https://codereview.chromium.org/1455003002/diff/1/lib/src/context.dart#newcode82
lib/src/context.dart:82: if (isAbsolute(part1) && !isRootRelative(part1) &&
part2 == null) {
On 2015/11/17 23:55:10, Bob Nystrom wrote:
> I'd move the null check first since that will be the fastest.

Done.