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

chrome/test/data/webui/md_history/md_history_browsertest.js

Index: chrome/test/data/webui/md_history/md_history_browsertest.js
diff --git a/chrome/test/data/webui/md_history/md_history_browsertest.js b/chrome/test/data/webui/md_history/md_history_browsertest.js
index e3caca0eb185f845eb31cba2b742fcf18cdd3c9f..3f11185a3f0796976ab0ce37b69c5a560ad0b162 100644
--- a/chrome/test/data/webui/md_history/md_history_browsertest.js
+++ b/chrome/test/data/webui/md_history/md_history_browsertest.js
@@ -33,6 +33,7 @@ MaterialHistoryBrowserTest.prototype = {
     'history_grouped_list_test.js',
     'history_item_test.js',
     'history_list_test.js',
+    'history_metrics_test.js',
     'history_overflow_menu_test.js',
     'history_routing_test.js',
     'history_supervised_user_test.js',
@@ -40,11 +41,26 @@ MaterialHistoryBrowserTest.prototype = {
     'history_toolbar_test.js'
   ]),
 
+  registerHistogramCallback_: function() {

[tsergeant, 2016/08/15 07:05:18]

I'm not a big fan of this:

Firstly, can it be local to the test, rather than applying to every test and
attaching results to window?

Secondly, since all you care about is the arguments passed to BrowserService, it
may be more appropriate to fake out the BrowserService instance and track the
calls in there.

[calamity, 2016/08/17 03:15:29]

Changed this as discussed

+    window.histogramMap = {};
+    registerMessageCallback(
+        'metricsHandler:recordInHistogram', this, function(args) {
+          if (!(args[0] in window.histogramMap))
+            window.histogramMap[args[0]] = {};
+
+          if (!(args[1] in window.histogramMap[args[0]]))
+            window.histogramMap[args[0]][args[1]] = 0;
+
+          window.histogramMap[args[0]][args[1]]++;
+        });
+  },
+
   /** @override */
   setUp: function() {
     PolymerTest.prototype.setUp.call(this);
 
     suiteSetup(function() {
+      this.registerHistogramCallback_();
       // Wait for the top-level app element to be upgraded.
       return waitForAppUpgrade().then(function() {
         $('history-app').queryState_.queryingDisabled = true;
@@ -55,8 +71,9 @@ MaterialHistoryBrowserTest.prototype = {
                 .$.toolbar.$['main-toolbar']
                 .getSearchField()
                 .isSearchFocused());
+
       });
-    });
+    }.bind(this));
   },
 };
 
@@ -85,6 +102,11 @@ TEST_F('MaterialHistoryBrowserTest', 'HistoryListTest', function() {
   mocha.run();
 });
 
+TEST_F('MaterialHistoryBrowserTest', 'HistoryMetricsTest', function() {
+  md_history.history_metrics_test.registerTests();
+  mocha.run();
+});
+
 TEST_F('MaterialHistoryBrowserTest', 'HistoryToolbarTest', function() {
   md_history.history_toolbar_test.registerTests();
   mocha.run();