Revert 273652 "Host extensions"

Revert 273652 "Host extensions"

gyp failure on Win:

Exception: Missing input files:

C:\b\build\slave\Win\build\src\remoting\host\extension.h

C:\b\build\slave\Win\build\src\remoting\host\extension_session.h


> Host extensions
> 
> This CL introduces HostExtension, an interface for classes that
> extend the host with non-core functionality.
> 
> Extensions are added to the ChromotingHost. They are used to compile
> the list of capabilities reported to the client, which can be used by
> the client to determine the availability of the extension.
> 
> When a client connects, a HostExtension has the opportunity to create
> an HostExtensionSession to hold client/extension state, and to handle
> extension messages from that client.
> 
> BUG=
> 
> Review URL: https://codereview.chromium.org/301453003

TBR=dcaiafa@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=273674

[mattm, 2014-05-30 00:06:02]

Committed patchset #1 manually as r273674 (tree was closed).