See

      https://docs.google.com/a/chromium.org/document/d/1fMxcEFiVj-H5vmuxhPqsxJAl98GS6_yZ-wqB6j9Wmy0/pub
for motivation and design.

Also add tests that it doesn't crash when deleted.

Also add the WebSocketDispatcherHost to the filters for IPC channels.

BUG=305515

Review URL: https://codereview.chromium.org/26544003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230712 0039d316-1c4b-4281-b951-d872f2087c98