Revert 155219 - [Chromoting] Refactoring DesktopEnvironment and moving screen/audio recorders to Cl…

Revert 155219 - [Chromoting] Refactoring DesktopEnvironment and moving screen/audio recorders to ClientSession.

This CL changes the way screen/audio recorders and event executors are managed. New DesktopEnvironmentFactory class is now used by ChromotingHost's owner to specify the kind of desktop environment (or virtual terminal) to be used by the host. Screen/audio recorders and event executors now owned by the ClientSession instance, so there is a separate set of recorders and stubs exists for each authenticated client session. Clients sessions can now be torn dowsn in parallel with the host shuttting down.

BUG=134694
TEST=remoting_unittests

Review URL: https://chromiumcodereview.appspot.com/10920019

TBR=alexeypa@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=155276