Move workflow function access to CategoryFunction class

This permits us to later move the workflow code into the server side,
moving it off the client.  We're not likely to ever support running
the project's workflow rules on the client in JavaScript.

Signed-off-by: Shawn O. Pearce <sop@google.com>

src/main/java/com/google/gerrit/server/ChangeManageServiceImpl.java

@@ -25,6 +25,7 @@ import com.google.gerrit.client.reviewdb.PatchSet;
 import com.google.gerrit.client.reviewdb.ReviewDb;
 import com.google.gerrit.client.rpc.Common;
 import com.google.gerrit.client.rpc.NoSuchEntityException;
+import com.google.gerrit.client.workflow.CategoryFunction;
 import com.google.gerrit.client.workflow.FunctionState;
 import com.google.gerrit.git.MergeQueue;
 import com.google.gwt.user.client.rpc.AsyncCallback;
@@ -90,9 +91,10 @@ public class ChangeManageServiceImpl extends BaseServiceImplementation
 
         final FunctionState fs = new FunctionState(change, allApprovals);
         for (ApprovalType c : Common.getGerritConfig().getApprovalTypes()) {
-          c.getCategory().getFunction().run(c, fs);
+          CategoryFunction.forCategory(c.getCategory()).run(c, fs);
         }
-        if (!actionType.getCategory().getFunction().isValid(me, actionType, fs)) {
+        if (!CategoryFunction.forCategory(actionType.getCategory()).isValid(me,
+            actionType, fs)) {
           throw new Failure(new IllegalStateException(actionType.getCategory()
               .getName()
               + " not permitted"));