[MD History] Add UMA stats for switching views and the CBD button.

chrome/browser/resources/md_history/app.js

Index: chrome/browser/resources/md_history/app.js
diff --git a/chrome/browser/resources/md_history/app.js b/chrome/browser/resources/md_history/app.js
index 4864f53a324ba2e72c44d2f7a96466da82f81573..790c53e1f8895fcce24b5915f07f759011a89392 100644
--- a/chrome/browser/resources/md_history/app.js
+++ b/chrome/browser/resources/md_history/app.js
@@ -9,7 +9,7 @@ Polymer({
     showSidebarFooter: Boolean,
 
     // The id of the currently selected page.
-    selectedPage_: {type: String, value: 'history', observer: 'unselectAll'},
+    selectedPage_: {type: String, observer: 'unselectAll'},
 
     // Whether domain-grouped history is enabled.
     grouped_: {type: Boolean, reflectToAttribute: true},
@@ -76,6 +76,7 @@ Polymer({
     'delete-selected': 'deleteSelected',
     'search-domain': 'searchDomain_',
     'history-close-drawer': 'closeDrawer_',
+    'history-view-changed': 'recordHistoryView_',
   },
 
   /** @override */
@@ -229,7 +230,7 @@ Polymer({
       /** @type {HistorySyncedDeviceManagerElement} */this
           .$$('history-synced-device-manager');
     if (syncedDeviceManagerElem)
-      syncedDeviceManagerElem.updateSignInState(isUserSignedIn);
+      syncedDeviceManagerElem.signInState = isUserSignedIn;
   },
 
   /**
@@ -267,6 +268,12 @@ Polymer({
    */
   selectedPageChanged_: function(selectedPage) {
     this.set('routeData_.page', selectedPage);
+
+    // Log the current view on the next animation frame to allow the iron-pages
+    // to detect that the synced-device-manager has been rendered.
+    requestAnimationFrame(function() {
+      this.recordHistoryView_();
+    }.bind(this));
   },
 
   /**
@@ -289,4 +296,36 @@ Polymer({
     if (drawer)
       drawer.close();
   },
+
+  /** @private */
+  recordHistoryView_: function() {
+    var histogramValue = HistoryViewHistogram.END;
+    switch (this.$.content.selectedItem.id) {

[tsergeant, 2016/08/17 06:03:09]

Why not just use this.selectedPage here? Then there's no need for the asyncery
at all.

You can use a default case to handle the fact that 'history' can also be the
empty string.

As an aside, we probably should try to normalise the value in selectedPage_ so
it can't be the empty string.

[calamity, 2016/08/18 03:11:15]

Done. Normalizing sounds... annoying and subtle. I'm not sure how that would
interact with the binding to the route. 

+      case 'history':
+        switch (this.queryState_.range) {
+          case HistoryRange.ALL_TIME:
+            histogramValue = HistoryViewHistogram.HISTORY;
+            break;
+          case HistoryRange.WEEK:
+            histogramValue = HistoryViewHistogram.GROUPED_WEEK;
+            break;
+          case HistoryRange.MONTH:
+            histogramValue = HistoryViewHistogram.GROUPED_MONTH;
+            break;
+        }
+        break;
+      case 'synced-devices':
+        var syncedDeviceManager =
+            /** @type {HistorySyncedDeviceManagerElement} */ this.$.content
+                .selectedItem;
+        histogramValue = syncedDeviceManager.signInState ?
+            HistoryViewHistogram.SYNCED_TABS :
+            HistoryViewHistogram.SIGNIN_PROMO;
+        break;
+    }
+
+    md_history.BrowserService.getInstance().recordHistogram(
+      'History.HistoryView', histogramValue, HistoryViewHistogram.END
+    );
+  },
 });