Show correct location from properties dialog

Fixes https://github.com/dart-lang/spark/issues/1303

@devoncarew
CC : @dinhviethoa

From Local File system
![image](https://f.cloud.github.com/assets/756988/2397149/8d22d718-a9e5-11e3-9a05-ddafdff0a834.png)

From Sync File System(Chromebook)
![image](https://f.cloud.github.com/assets/756988/2397183/2b116f8e-a9e6-11e3-84b9-85b2831ff0b6.png)