Revert 228681 "DevTools: support beforeunload lifecycle for DevT..."

New test DevToolsBeforeUnloadTest.TestBeforeUnloadEvents times out on XP
Tests (dbg) 4.

http://build.chromium.org/p/chromium.win/builders/XP%20Tests%20%28dbg%29%284%29/builds/37464/steps/browser_tests/logs/stdio

> DevTools: support beforeunload lifecycle for DevTools window
> 
> This patch teaches DevTools window to send beforeunload events to
> its frontend. This events won't be send if the inspected webcontents
> got closed - additional work is needed to handle this case.
> 
> BUG=289552
> TBR=pfeldman
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=228346
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=228473
> 
> Review URL: https://codereview.chromium.org/23766027

TBR=lushnikov@chromium.org

Review URL: https://codereview.chromium.org/27372002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228717 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228717