Revert 248280 "Fix a crash in content-shell headless mode with -..."

Speculative revert to fix a flaky crash in Blink layout tests:

http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40ToT%20Blink&showExpectations=true&tests=fast%2Fforms%2Fimplicit-submission.html


> Fix a crash in content-shell headless mode with --dump-render-tree
> 
> Currently the platform specific state is not cleanedup in headless
> mode and that leads to a crash upon content-shell exit.
> 
> This patch deinitialize the platform specific state in Shell
> destructor so that it will delete the aura::WindowTreeHost which
> will delete the compositor.
> 
> BUG=338919
> 
> Review URL: https://codereview.chromium.org/149593002

TBR=sudarsana.nagineni@intel.com

Review URL: https://codereview.chromium.org/134773007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248304 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248304