Wait for pluginRestApi to be set before calling getCheckers

Change-Id: I6f900d3d960ef09c81caec5866d13ba759555080
diff --git a/gr-checks/gr-checkers-list.js b/gr-checks/gr-checkers-list.js
index 2542832..d2c7256 100644
--- a/gr-checks/gr-checkers-list.js
+++ b/gr-checks/gr-checkers-list.js
@@ -9,7 +9,15 @@
   Polymer({
     is: 'gr-checkers-list',
     properties: {
-      pluginRestApi: Object,
+      /**
+       * Add observer on pluginRestApi to call getCheckers when it's defined
+       * as initially getCheckers was being called before pluginRestApi was
+       * initialised by gr-checks-view
+       */
+      pluginRestApi: {
+        type: Object,
+        observer: '_getCheckers'
+      },
       // Checker that will be passed to the editOverlay modal
       checker: Object,
       _checkers: Array,
@@ -51,10 +59,6 @@
       '_showCheckers(_checkers, _filter)',
     ],
 
-    attached() {
-      this._getCheckers();
-    },
-
     _contains(target, keyword) {
       return target.toLowerCase().includes(keyword.toLowerCase().trim());
     },
@@ -117,8 +121,9 @@
       }
     },
 
-    _getCheckers() {
-      this.pluginRestApi.fetchJSON({
+    _getCheckers(pluginRestApi) {
+      if (!pluginRestApi) return;
+      pluginRestApi.fetchJSON({
         method: 'GET',
         url: GET_CHECKERS_URL,
       }).then(checkers => {