A file URI can now be created directly using the constructor Uri.file.
The file path for a file URI can now be extracted using the toFilePath() method.
The path strings involved use either Windows or non-Windows
semantics. Both the Uri.file constructor and the toFilePath()
method have optional anamed arguments for specifying the
semantics. The default semantic is determined from the platform
Dart is running on.
R=ahe@google.com, whesse@google.com
BUG=
Review URL: https://codereview.chromium.org//21039005
git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@25872 260f80e4-7a28-3924-810f-c04153c831b5
sgjesse@google.com