Expose method to alter visual state of actions

This change allows clients to alter which actions are styled as
“primary”.

Change-Id: I9876ba0a9939fbfd460e17b09ee5c338cb2bf40e

polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.html

diff --git a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.html b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.html
index b0f5a5c..a8df10b 100644
--- a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.html
+++ b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.html
@@ -128,6 +128,7 @@
         var rebaseAction = {
           __key: 'rebase',
           __type: 'revision',
+          __primary: false,
           label: 'Rebase',
           method: 'POST',
           title: 'Rebase onto tip of branch or parent change',
@@ -173,6 +174,7 @@
         var action = {
           __key: 'cherrypick',
           __type: 'revision',
+          __primary: false,
           enabled: true,
           label: 'Cherry Pick',
           method: 'POST',
@@ -232,6 +234,7 @@
         var action = {
           __key: 'revert',
           __type: 'change',
+          __primary: false,
           enabled: true,
           label: 'Revert',
           method: 'POST',