Revert 168053 "Fix a crash when spell checker is triggered for a..."

May have caused crashes on Android bot.

> Fix a crash when spell checker is triggered for an editable element which is in an author ShadowRoot of an INPUT element.
> 
> enclosingTextFormControl() should handle only elements in UA ShadowRoot.
> 
> BUG=343040
> TEST=automated
> 
> Review URL: https://codereview.chromium.org/181273002

TBR=tkent@chromium.org

Review URL: https://codereview.chromium.org/183793005

git-svn-id: svn://svn.chromium.org/blink/trunk@168061 bbb929c8-8fbe-4397-9dbb-9b2b20218538