[DevTools] Separate ScreenCaptureModel out of ResourceTreeModel.

third_party/WebKit/Source/devtools/front_end/emulation/DeviceModeModel.js

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 /**
  * @implements {SDK.TargetManager.Observer}
  * @unrestricted
  */
 Emulation.DeviceModeModel = class {
   /**
    * @param {function()} updateCallback
@@ skipping 314 matching lines @@
 
   /**
    * @override
    * @param {!SDK.Target} target
    */
   targetRemoved(target) {
     if (this._target === target)
       this._target = null;
   }
 
+  /**
+   * @return {?SDK.Target}
+   */
+  target() {
+    return this._target;
+  }
+
   _scaleSettingChanged() {
     this._calculateAndEmulate(false);
   }
 
   _widthSettingChanged() {
     this._calculateAndEmulate(false);
   }
 
   _heightSettingChanged() {
     this._calculateAndEmulate(false);
@@ skipping 287 matching lines @@
 
 Emulation.DeviceModeModel.MinDeviceSize = 50;
 Emulation.DeviceModeModel.MaxDeviceSize = 9999;
 
 
 Emulation.DeviceModeModel._defaultMobileUserAgent =
     'Mozilla/5.0 (Linux; Android 6.0; Nexus 5 Build/MRA58N) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/%s Mobile Safari/537.36';
 Emulation.DeviceModeModel._defaultMobileUserAgent =
     SDK.MultitargetNetworkManager.patchUserAgentWithChromeVersion(Emulation.DeviceModeModel._defaultMobileUserAgent);
 Emulation.DeviceModeModel.defaultMobileScaleFactor = 2;