[Media Router] Add UMA metrics to record the load time for route controls

chrome/browser/resources/media_router/elements/route_controls/route_controls.js

Index: chrome/browser/resources/media_router/elements/route_controls/route_controls.js
diff --git a/chrome/browser/resources/media_router/elements/route_controls/route_controls.js b/chrome/browser/resources/media_router/elements/route_controls/route_controls.js
index 4d3a65bc61b8b87fbab79581dc093b0bd3a33a32..420e31eb9fd5be27b01145bc32457441c2cd3068 100644
--- a/chrome/browser/resources/media_router/elements/route_controls/route_controls.js
+++ b/chrome/browser/resources/media_router/elements/route_controls/route_controls.js
@@ -40,6 +40,15 @@ Polymer({
     },
 
     /**
+     * The time when the initial media status was loaded.
+     * @private {?Date}
+     */
+    initialLoadTime_: {
+      type: Date,
+      value: null,
+    },
+
+    /**
      * Set to true when the user is dragging the seek bar. Updates for the
      * current time from the browser will be ignored when set to true.
      * @private {boolean}
@@ -60,6 +69,16 @@ Polymer({
     },
 
     /**
+     * The time when the route details view was opened.
+     * @type {?Date}
+     */
+    routeDetailsOpenTime: {
+      type: Date,
+      value: null,
+      observer: 'onRouteDetailsOpenTimeSet_',

[imcheng, 2017/06/02 23:53:13]

We can use maybeReportLoadTime_ here. Then we won't need
onRouteDetailsOpenTimeSet_. But then if we set openTime on route details during
construction, then I don't think we need the observer here.

[takumif, 2017/06/03 01:31:14]

Right, the observer is no longer necessary. Removed.

+    },
+
+    /**
      * The status of the media route shown.
      * @type {!media_router.RouteStatus}
      */
@@ -148,6 +167,19 @@ Polymer({
   },
 
   /**
+   * Notify the browser the time it took from opening the route details view to
+   * loading the route controller if the data is available.
+   *
+   * @private
+   */
+  maybeReportLoadTime_: function() {
+    if (this.initialLoadTime_ && this.routeDetailsOpenTime) {
+      var timeMs = this.initialLoadTime_ - this.routeDetailsOpenTime;
+      media_router.browserApi.reportWebUIRouteControllerLoaded(timeMs);
+    }
+  },
+
+  /**
    * Called when the user toggles the mute status of the media. Sends a mute or
    * unmute command to the browser.
    *
@@ -181,6 +213,15 @@ Polymer({
   },
 
   /**
+   * Called when |routeDetailsOpenTime| is set.
+   *
+   * @private
+   */
+  onRouteDetailsOpenTimeSet_: function() {
+    this.maybeReportLoadTime_();
+  },
+
+  /**
    * Updates seek and volume bars if the user is not currently dragging on
    * them.
    * @param {!media_router.RouteStatus} newRouteStatus
@@ -197,6 +238,10 @@ Polymer({
     if (newRouteStatus.description !== '') {
       this.displayedDescription_ = newRouteStatus.description;
     }
+    if (!this.initialLoadTime_) {
+      this.initialLoadTime_ = new Date();

[imcheng, 2017/06/02 23:53:13]

Date.now()

[takumif, 2017/06/03 01:31:14]

Done.

+      this.maybeReportLoadTime_();
+    }
   },
 
   /**