Revert 57112 - Rename (Host|Client)Message to Chromoting(Host|Client)Message....

Revert 57112 - Rename (Host|Client)Message to Chromoting(Host|Client)Message.

Rename HostMessage and ClientMessage to Chromoting{Host|Client}Message to
avoid conflicts with messages in X11.

Actually, only ClientMessage needs to be changed due to conflict, but HostMessage is changed to keep the names consistent.

BUG=none
TEST=remoting unittests

Review URL: http://codereview.chromium.org/3161034

TBR=garykac@chromium.org

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=57115