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

[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.

This is the 4th attempt to land this change. This version includes:
- |ClientSession| objects are torn down asynchronously now.
- |ClientSession| objects are ref-counted to facilitate the asynchronous shutdown. They still have to be used and destroyed on the network thread.
- |ChromotingHost| now waits until all connections are torn down before deleting the session manager.
- The unit tests were fixed to run message loops until all asynchronous object have been destroyed.
- |ClientSessionTest.ClampMouseEvents| makes sure that the expectations are destroyed when leaving TEST_F scope so that ASAN is not getting confused.

BUG=134694
TEST=remoting_unittests

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=156398

[alexeypa (please no reviews), 2012-09-12 16:11:53]

Relanding r156297. r156297 didn't go though the try bots because the bots
weren't able to apply the patch for some reason. --revision=<base revision>
didn't help. I'm investigating why.

Meanwhile this CL was sent to try bots just fine, so we will get enough coverage
before submitting it.

Patch #1 is the original CL. Patch #2 is a fix for compilation issue. PTAL.

[simonmorris, 2012-09-12 18:02:10]

lgtm

[commit-bot: I haz the power, 2012-09-12 18:29:10]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/alexeypa@chromium.org/10916263/7002

[commit-bot: I haz the power, 2012-09-12 22:18:03]

Failed to apply patch for remoting/host/plugin/host_script_object.cc:
While running patch -p1 --forward --force;
patching file remoting/host/plugin/host_script_object.cc
Hunk #2 succeeded at 93 with fuzz 1.
Hunk #3 succeeded at 518 (offset 6 lines).
Hunk #4 succeeded at 550 (offset 6 lines).
Hunk #5 succeeded at 583 (offset 6 lines).
Hunk #6 FAILED at 870.
Hunk #7 FAILED at 900.
2 out of 7 hunks FAILED -- saving rejects to file
remoting/host/plugin/host_script_object.cc.rej