Revert 234708 "When DWM compositing is disabled (i.e. XP, RDP) e..."

> When DWM compositing is disabled (i.e. XP, RDP) ensure that windowed NPAPI plugins don't cover UI dialogs. This includes things like omnibox, star window, profile selector, and bookmark editor.
> 
> The solution is to start watching the root window as well as the parent window.
> BUG=299224
> R=ben@chromium.org
> 
> Review URL: https://codereview.chromium.org/69833002

TBR=jam@chromium.org

Review URL: https://codereview.chromium.org/70443004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234770 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234770