Fixing resizing performance issue in split view 

Resizing in split view is too slow because the width of the codemirror editor is changing on resizing and it has to render it's contents every time.

We change the width to fixed size (3000px) on resizing start and restore to default at the end so codemirror doesn't render it's contents anymore :)
Indentation is still off for these two lines. If you edit this file in Brackets, you should be seeing JSLint error on this line.