New Dartium: fix editor panel resizing randomly when switching between files

@dinhviethoa

The problem looked like this:

![screen shot 2014-05-26 at 1 57 27 am](https://cloud.githubusercontent.com/assets/5606182/3080671/fe7bc970-e4b3-11e3-8b62-af551696d82a.png)

![screen shot 2014-05-26 at 1 59 57 am](https://cloud.githubusercontent.com/assets/5606182/3080683/29d37bae-e4b4-11e3-8797-a4228da5ea54.png)

The duplicate selection in the file tree view still remains - I didn't look into it.