Add normalizePath to Uri class.

Add normalizePath to Uri class.

The algorithm for removing '.' and '..' from a path is only available through the [resolve] method.
This change makes it available directly as a function on a Uri, returning a new Uri if necessary.
The current workaround is to do:
  var normalizedUri = new Uri().resolveUri(originalUri);

R=sgjesse@google.com

Committed: https://code.google.com/p/dart/source/detail?r=45163

[Lasse Reichstein Nielsen, 2015-04-15 09:32:41]

lrn@google.com changed reviewers:
+ sgjesse@google.com

[Lasse Reichstein Nielsen, 2015-04-15 09:32:42]

Will add tests.

[Søren Gjesse, 2015-04-15 09:36:01]

lgtm with tests

[Lasse Reichstein Nielsen, 2015-04-15 11:56:42]

Committed patchset #2 (id:20001) manually as 45163 (presubmit successful).