Add metrics for Webstore Gallery Widget app

components/chrome_apps/webstore_widget/app/main.js

Index: components/chrome_apps/webstore_widget/app/main.js
diff --git a/components/chrome_apps/webstore_widget/app/main.js b/components/chrome_apps/webstore_widget/app/main.js
index 1151da84a367588a199a5f6da0440fa529f86c89..8ada750b1506c200c131b721ac1eeb81651665ce 100644
--- a/components/chrome_apps/webstore_widget/app/main.js
+++ b/components/chrome_apps/webstore_widget/app/main.js
@@ -68,20 +68,50 @@ function createPlatformDelegate(strings) {
 
     metricsImpl: {
       /**
+       * Map from interval name to interval start timestamp.
+       * @type {Object<string, Date>}
+       */
+      intervals: {},
+
+      /**
        * @param {string} enumName
        * @param {number} value
        * @param {number} enumSize
        */
-      recordEnum: function(enumName, value, enumSize) {},
+      recordEnum: function(enumName, value, enumSize) {
+        var index = (value >= 0 && value < enumSize) ? value : enumSize - 1;
+        chrome.metricsPrivate.recordValue({
+          'metricName': 'WebstoreWidgetApp.' + enumName,
+          'type': 'histogram-linear',
+          'min': 1,
+          'max': enumSize,
+          'buckets': enumSize

[Ilya Sherman, 2015/06/25 21:40:29]

Hmm, I think that either max should be "enumSize - 1", or buckets should be
"enumSize".  Does the metricsPrivate API not have a method to emit to an
enumerated histogram?  If not, perhaps it's worth adding one, so that we only
need to get this implementation detail right once?

[tbarzic, 2015/06/25 22:31:09]

This is how these values are recorded in File Manager metrics..

The issue is that values in these enums start at 0. To work around this, the
underflow bucket is used as a real bucket (and values that would usually be sent
there are moved to overflow bucket).
So we end up with one bucket less than usual.
Though, maybe I could just set min to 0 and max to enumSize - 1?

[Ilya Sherman, 2015/06/25 22:36:31]

It's fine for the underflow bucket to be emitted to -- that's what most
enumerated histograms do.  But, you still need to leave space for the overflow
bucket.  So, if you're actually emitting to N buckets, and one of those N
buckets is the underflow bucket, then you need N + 1 buckets to be allocated,
where the extra bucket is the overflow bucket.

[tbarzic, 2015/06/25 22:46:12]

Done.

+        }, index);
+      },
 
       /** @param {string} actionName */
-      recordUserAction: function(actionName) {},
+      recordUserAction: function(actionName) {
+        chrome.metricsPrivate.recordUserAction(
+            'WebstoreWidgetApp.' + actionName);

[Ilya Sherman, 2015/06/25 21:40:30]

Please update actions.xml with any actions that you're adding.

[tbarzic, 2015/06/25 22:31:09]

Done.

+      },
 
       /** @param {string} intervalName */
-      startInterval: function(intervalName) {},
+      startInterval: function(intervalName) {
+        this.intervals[intervalName] = Date.now();
+      },
 
       /** @param {string} intervalName */
-      recordInterval: function(intervalName) {}
+      recordInterval: function(intervalName) {
+        if (!intervalName in this.intervals) {
+          console.error('Interval \'' + intervalName + '\' not started');
+          return;
+        }
+
+       chrome.metricsPrivate.recordTime(
+           'WebstoreWidgetApp.' + intervalName,
+           Date.now() - this.intervals[intervalName]);
+        delete this.intervals[intervalName];
+      }
     },
 
     /**