Timeline: bring back tracking of TimelinePageReloadStarted action

This is a follow-up https://codereview.chromium.org/2883143003 that
brings back tracking of timelines started with page reload (the meaning
of which is somewhat different now).

Change-Id: I8cde7aba72290dd99b42ddb36d2b1f3a989d0a9c
Reviewed-on: https://chromium-review.googlesource.com/531875Reviewed-by: Alexei Filippov <alph@chromium.org>
Commit-Queue: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#478809}

third_party/WebKit/Source/devtools/front_end/timeline/TimelinePanel.js

@@ -551,7 +551,6 @@ Timeline.TimelinePanel = class extends UI.Panel {
 
     this._pendingPerformanceModel = new Timeline.PerformanceModel();
     this._controller = new Timeline.TimelineController(tracingManagers[0], this._pendingPerformanceModel, this);
-    Host.userMetrics.actionTaken(Host.UserMetrics.Action.TimelineStarted);
     this._setUIControlsEnabled(false);
     this._hideLandingPage();
     return this._controller.startRecording(recordingOptions, enabledTraceProviders)
@@ -590,6 +589,7 @@ Timeline.TimelinePanel = class extends UI.Panel {
     if (this._state === Timeline.TimelinePanel.State.Idle) {
       this._recordingPageReload = false;
       this._startRecording();
+      Host.userMetrics.actionTaken(Host.UserMetrics.Action.TimelineStarted);
     } else if (this._state === Timeline.TimelinePanel.State.Recording) {
       this._stopRecording();
     }
@@ -600,6 +600,7 @@ Timeline.TimelinePanel = class extends UI.Panel {
       return;
     this._recordingPageReload = true;
     this._startRecording();
+    Host.userMetrics.actionTaken(Host.UserMetrics.Action.TimelinePageReloadStarted);
   }
 
   _onClearButton() {