Allow "Default View" policies to be set to Public

Summary: Ref T603. Currently, we hard-code defense against setting policies to "Public" in several places, and special case only the CAN_VIEW policy. In fact, other policies (like Default View) should also be able to be set to public. Instead of hard-coding this, move it to the capability definitions.

Test Plan: Set default view policy in Maniphest to "Public", created a task, verified default policy.

Reviewers: btrahan, asherkin

Reviewed By: asherkin

CC: asherkin, aran

Maniphest Tasks: T603

Differential Revision: https://secure.phabricator.com/D7276

src/applications/meta/controller/PhabricatorApplicationEditController.php

@@ -51,9 +51,9 @@ final class PhabricatorApplicationEditController
           continue;
         }
 
-        if ($new == PhabricatorPolicies::POLICY_PUBLIC &&
-            $capability != PhabricatorPolicyCapability::CAN_VIEW) {
-          // Can't set policies other than "view" to public.
+        $capobj = PhabricatorPolicyCapability::getCapabilityByKey($capability);
+        if (!$capobj || !$capobj->shouldAllowPublicPolicySetting()) {
+          // Can't set non-public policies to public.
           continue;
         }