Add a class for propagating request scoping to different threads

Request scopes are all implemented with ThreadLocals, which meant that
RequestScoped data would not be available in any new threads created
from the main request thread. Add a class to wrap Runnables and Callables
so tasks that depend on request scoped objects can be inserted in a
WorkQueue.

Include ScopePropagator implementations for all request scope
types. The GuiceRequestScopePropagator will forward
materialized instances of CurrentUser, RemotePeer SocketAddress,
and the CannonicalWebUrl. To support this, CanonicalWebUrlModule is
not bound as a SINGLETON anymore and HttpIdentifiedUserProvider
implementation now relies on CurrentUser, instead of the WebSession.
This was needed because some fields in the HttpRequest object are
cleared after the request is finished, but possibly before
the propagated request context has been processed. The non guice
request scopes do not have this problem, so they can reconstruct the
needed objects in the propagated context.

Change-Id: I586cd1c91727e2cb8abb166f23fc504e9949a944

gerrit-sshd/src/main/java/com/google/gerrit/sshd/SshModule.java

@@ -32,6 +32,7 @@ import com.google.gerrit.server.git.QueueProvider;
 import com.google.gerrit.server.git.WorkQueue;
 import com.google.gerrit.server.project.ProjectControl;
 import com.google.gerrit.server.ssh.SshInfo;
+import com.google.gerrit.server.util.RequestScopePropagator;
 import com.google.gerrit.sshd.args4j.AccountGroupIdHandler;
 import com.google.gerrit.sshd.args4j.AccountGroupUUIDHandler;
 import com.google.gerrit.sshd.args4j.AccountIdHandler;
@@ -57,6 +58,7 @@ public class SshModule extends FactoryModule {
   @Override
   protected void configure() {
     bindScope(RequestScoped.class, SshScope.REQUEST);
+    bind(RequestScopePropagator.class).to(SshScope.Propagator.class);
 
     configureRequestScope();
     configureCmdLineParser();