Make it possible to delete ServiceResolverImpl on callback

ServiceResolverImpl was updating its state to reset itself after calling its
callback. Make it possible to delete it from within the callback by removing
that and moving it to StartResolving().

BUG=

Review URL: https://codereview.chromium.org/25646002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226564 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226564