Revert "Revert "Use only Gerrit.install as a plugin loaded signal""

This reverts commit 96d037968f.

It also contains the underyling fix for loading plugins correctly. The
importHref function expected functions for onload and onerror arguments
and passing null instead was causing the unexplained behavior.

Change-Id: Ic2a36d9bfcf85e5769c26ab49caf15e572d9463e

polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata-it_test.html

@@ -93,7 +93,8 @@ limitations under the License.
           plugin: {
             js_resource_paths: [],
             html_resource_paths: [
-              new URL('test/plugin.html', window.location.href).toString(),
+              new URL('test/plugin.html?' + Math.random(),
+                      window.location.href).toString(),
             ],
           },
         };

polygerrit-ui/app/elements/plugins/gr-endpoint-decorator/gr-endpoint-decorator_test.html

@@ -24,6 +24,8 @@ limitations under the License.
 <link rel="import" href="gr-endpoint-decorator.html">
 <link rel="import" href="../gr-endpoint-param/gr-endpoint-param.html">
 
+<script>void(0);</script>
+
 <test-fixture id="basic">
   <template>
     <gr-endpoint-decorator name="foo">

polygerrit-ui/app/elements/plugins/gr-plugin-host/gr-plugin-host.js

@@ -47,12 +47,12 @@
      * States that it expects no more than 3 parameters, but that's not true.
      * @todo (beckysiegel) check Polymer annotations and submit change.
      */
-
     _importHtmlPlugins(plugins) {
       for (const url of plugins) {
+        // onload (second param) needs to be a function. When null or undefined
+        // were passed, plugins were not loaded correctly.
         this.importHref(
-            this._urlFor(url), Gerrit._pluginInstalled, Gerrit._pluginInstalled,
-            true);
+            this._urlFor(url), () => {}, Gerrit._pluginInstalled, true);
       }
     },
 

polygerrit-ui/app/elements/plugins/gr-plugin-host/gr-plugin-host_test.html

@@ -23,6 +23,8 @@ limitations under the License.
 <link rel="import" href="../../../test/common-test-setup.html"/>
 <link rel="import" href="gr-plugin-host.html">
 
+<script>void(0);</script>
+
 <test-fixture id="basic">
   <template>
     <gr-plugin-host></gr-plugin-host>
@@ -60,22 +62,38 @@ limitations under the License.
       element.config = {
         plugin: {html_resource_paths: ['foo/bar', 'baz']},
       };
-      assert.isTrue(element.importHref.calledWith(
-          '/foo/bar', Gerrit._pluginInstalled, Gerrit._pluginInstalled, true));
-      assert.isTrue(element.importHref.calledWith(
-          '/baz', Gerrit._pluginInstalled, Gerrit._pluginInstalled, true));
+      assert.equal(element.importHref.firstCall.args[0], '/foo/bar');
+      assert.equal(element.importHref.firstCall.args[2],
+          Gerrit._pluginInstalled);
+      assert.isTrue(element.importHref.firstCall.args[3]);
+
+      assert.equal(element.importHref.secondCall.args[0], '/baz');
+      assert.equal(element.importHref.secondCall.args[2],
+          Gerrit._pluginInstalled);
+      assert.isTrue(element.importHref.secondCall.args[3]);
     });
 
     test('imports relative html plugins from config with a base url', () => {
       sandbox.stub(element, 'getBaseUrl').returns('/the-base');
       element.config = {
         plugin: {html_resource_paths: ['foo/bar', 'baz']}};
-      assert.isTrue(element.importHref.calledWith(
-          '/the-base/foo/bar', Gerrit._pluginInstalled, Gerrit._pluginInstalled,
-          true));
-      assert.isTrue(element.importHref.calledWith(
-          '/the-base/baz', Gerrit._pluginInstalled, Gerrit._pluginInstalled,
-          true));
+      assert.equal(element.importHref.firstCall.args[0], '/the-base/foo/bar');
+      assert.equal(element.importHref.firstCall.args[2],
+          Gerrit._pluginInstalled);
+      assert.isTrue(element.importHref.firstCall.args[3]);
+
+      assert.equal(element.importHref.secondCall.args[0], '/the-base/baz');
+      assert.equal(element.importHref.secondCall.args[2],
+          Gerrit._pluginInstalled);
+      assert.isTrue(element.importHref.secondCall.args[3]);
+    });
+
+    test('inportHref is not called with null callback functions', () => {
+      const plugins = ['path/to/plugin'];
+      element._importHtmlPlugins(plugins);
+      assert.isTrue(element.importHref.calledOnce);
+      assert.isFunction(element.importHref.lastCall.args[1]);
+      assert.isFunction(element.importHref.lastCall.args[2]);
     });
 
     test('imports absolute html plugins from config', () => {
@@ -87,12 +105,17 @@ limitations under the License.
           ],
         },
       };
-      assert.isTrue(element.importHref.calledWith(
-          'http://example.com/foo/bar', Gerrit._pluginInstalled,
-          Gerrit._pluginInstalled, true));
-      assert.isTrue(element.importHref.calledWith(
-          'https://example.com/baz', Gerrit._pluginInstalled,
-          Gerrit._pluginInstalled, true));
+      assert.equal(element.importHref.firstCall.args[0],
+          'http://example.com/foo/bar');
+      assert.equal(element.importHref.firstCall.args[2],
+          Gerrit._pluginInstalled);
+      assert.isTrue(element.importHref.firstCall.args[3]);
+
+      assert.equal(element.importHref.secondCall.args[0],
+          'https://example.com/baz');
+      assert.equal(element.importHref.secondCall.args[2],
+          Gerrit._pluginInstalled);
+      assert.isTrue(element.importHref.secondCall.args[3]);
     });
 
     test('adds js plugins from config to the body', () => {
@@ -138,10 +161,15 @@ limitations under the License.
           html_resource_paths: ['some'],
         },
       };
-      assert.isTrue(element.importHref.calledWith(
-          '/oof', Gerrit._pluginInstalled, Gerrit._pluginInstalled, true));
-      assert.isTrue(element.importHref.calledWith(
-          '/some', Gerrit._pluginInstalled, Gerrit._pluginInstalled, true));
+      assert.equal(element.importHref.firstCall.args[0], '/oof');
+      assert.equal(element.importHref.firstCall.args[2],
+          Gerrit._pluginInstalled);
+      assert.isTrue(element.importHref.firstCall.args[3]);
+
+      assert.equal(element.importHref.secondCall.args[0], '/some');
+      assert.equal(element.importHref.secondCall.args[2],
+          Gerrit._pluginInstalled);
+      assert.isTrue(element.importHref.secondCall.args[3]);
     });
   });
 </script>