refactor: serve hide CSS from eejsBlock_styles via hideCSS helper

ep.json

@@ -1,12 +1,14 @@
 {
-  "disables": ["@feature:error-gritter"],
-  "parts":[
+  "disables": [
+    "@feature:error-gritter"
+  ],
+  "parts": [
     {
       "name": "ep_disable_error_messages",
-      "hooks": {},
-      "client_hooks": {
-         "postAceInit":"ep_disable_error_messages/static/js/disable_error_messages:postAceInit"
-      }
+      "hooks": {
+        "eejsBlock_styles": "ep_disable_error_messages/index:eejsBlock_styles"
+      },
+      "client_hooks": {}
     }
   ]
 }

index.js

@@ -0,0 +1,9 @@
+'use strict';
+
+const {hideCSS} = require('ep_plugin_helpers');
+
+// Hide error gritter notifications on the pad page. Previously this
+// injected the CSS client-side from postAceInit; serving it from
+// eejsBlock_styles instead makes it available before the editor
+// initialises, so users never see the error popup flash on load.
+exports.eejsBlock_styles = hideCSS('#gritter-container > .error');

package.json

@@ -29,5 +29,8 @@
   "repository": {
     "type": "git",
     "url": "https://github.com/ether/ep_disable_error_messages.git"
+  },
+  "dependencies": {
+    "ep_plugin_helpers": "^0.5.0"
   }
 }