Revert 256115 "Don't leak ExternalInstallDialogDelegate if the o..."

> Don't leak ExternalInstallDialogDelegate if the owning profile is destroyed.
> 
> BUG=346412
> 
> Review URL: https://codereview.chromium.org/189003006

TBR=rdevlin.cronin@chromium.org

Review URL: https://codereview.chromium.org/193573003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256130 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256130