[DevTools] Turn TracingManager into SDKModel.

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

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2012 Intel Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 526 matching lines @@
   _setUIControlsEnabled(enabled) {
     this._recordingOptionUIControls.forEach(control => control.setEnabled(enabled));
   }
 
   /**
    * @param {boolean} userInitiated
    * @return {!Promise}
    */
   _startRecording(userInitiated) {
     console.assert(!this._statusPane, 'Status pane is already opened.');
-    var mainTarget = SDK.targetManager.mainTarget();
-    if (!mainTarget)
+    var tracingManagers = SDK.targetManager.models(SDK.TracingManager);
+    if (!tracingManagers.length)
       return Promise.resolve();
     this._setState(Timeline.TimelinePanel.State.StartPending);
     this._showRecordingStarted();
 
     this._autoRecordGeneration = userInitiated ? null : Symbol('Generation');
     var enabledTraceProviders = Extensions.extensionServer.traceProviders().filter(
         provider => Timeline.TimelinePanel._settingForTraceProvider(provider).get());
 
     const recordingOptions = {
       enableJSSampling: !this._disableCaptureJSProfileSetting.get(),
       capturePictures: this._captureLayersAndPicturesSetting.get(),
       captureFilmStrip: this._showScreenshotsSetting.get()
     };
 
     this._pendingPerformanceModel = new Timeline.PerformanceModel();
-    this._controller = new Timeline.TimelineController(mainTarget, this._pendingPerformanceModel, this);
+    this._controller = new Timeline.TimelineController(tracingManagers[0], this._pendingPerformanceModel, this);
     Host.userMetrics.actionTaken(
         userInitiated ? Host.UserMetrics.Action.TimelineStarted : Host.UserMetrics.Action.TimelinePageReloadStarted);
     this._setUIControlsEnabled(false);
     this._hideLandingPage();
     return this._controller.startRecording(recordingOptions, enabledTraceProviders)
         .then(() => this._recordingStarted());
   }
 
   _stopRecording() {
     if (this._statusPane) {
@@ skipping 764 matching lines @@
         return true;
       case 'timeline.jump-to-next-frame':
         panel._jumpToFrame(1);
         return true;
     }
     return false;
   }
 };
 
 Timeline.TimelinePanel._traceProviderSettingSymbol = Symbol('traceProviderSetting');