Add tracking to buttons

Example for when you click the "reply" button:
Reporting: button-click: main gr-change-view div#maincontent section
div#mainchangeinfo div#commitandrelated div div gr-button#replybtn

Change-Id: I0ce4f574e76b8d9c9c1f4fd87db026d86895f97f

polygerrit-ui/app/elements/shared/gr-button/gr-button.html

@@ -21,6 +21,7 @@ limitations under the License.
 <link rel="import" href="../../../behaviors/keyboard-shortcut-behavior/keyboard-shortcut-behavior.html">
 <link rel="import" href="/bower_components/paper-button/paper-button.html">
 <link rel="import" href="../../../styles/shared-styles.html">
+<link rel="import" href="../../core/gr-reporting/gr-reporting.html">
 
 <dom-module id="gr-button">
   <template strip-whitespace>
@@ -160,6 +161,7 @@ limitations under the License.
       <slot></slot>
       <i class="downArrow"></i>
     </paper-button>
+    <gr-reporting id="reporting"></gr-reporting>
   </template>
   <script src="gr-button.js"></script>
 </dom-module>

polygerrit-ui/app/elements/shared/gr-button/gr-button.js

@@ -90,6 +90,19 @@
         e.preventDefault();
         e.stopImmediatePropagation();
       }
+      let el = this.root;
+      let path = '';
+      while (el = el.parentNode || el.host) {
+        if (el.tagName && el.tagName.startsWith('GR-APP')) {
+          break;
+        }
+        if (el.tagName) {
+          const idString = el.id ? '#' + el.id : '';
+          path = el.tagName + idString + ' ' + path;
+        }
+      }
+      this.$.reporting.reportInteraction('button-click',
+          path.trim().toLowerCase());
     }
 
     _disabledChanged(disabled) {

polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-action-context_test.html

@@ -88,13 +88,17 @@ limitations under the License.
       assert.equal(div.textContent, 'foobar');
     });
 
-    test('button', () => {
+    test('button', done => {
       const clickStub = sandbox.stub();
       const button = instance.button('foo', {onclick: clickStub});
+      // If you don't attach a Polymer element to the DOM, then the ready()
+      // callback will not be called and then e.g. this.$ is undefined.
+      Polymer.dom(document.body).appendChild(button);
       MockInteractions.tap(button);
       flush(() => {
         assert.isTrue(clickStub.called);
         assert.equal(button.textContent, 'foo');
+        done();
       });
     });