Merge 177997

Merge 177997
> drive: Deal with the root directory same as others in MoveOperation.
> 
> Our current implementation of file moving is done in the following logic:
> "if(source!=root) RemoveFrom(source); if(target!=root) AddTo(target)"
> implicitly assuming "belonging to nowhere" means belonging to root.
> But this is not the case.
> 
> This patch removes the "if !=root" checks and treats the root as same as other directories.
> 
> BUG=169420
> TEST=Manually test the steps in the bug report.
> 
> Review URL: https://chromiumcodereview.appspot.com/12039005

TBR=kinaba@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=178494