[DevTools] Promote Device Mode v2 to default experiments.

third_party/WebKit/Source/devtools/front_end/emulation/deviceModeView.css

 /*
  * 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.
  */
 
 :host {
     overflow: hidden;
     align-items: stretch;
     flex: auto;
@@ skipping 24 matching lines @@
 
 .device-mode-media-container {
     flex: none;
     overflow: hidden;
 }
 
 .device-mode-content-area {
     flex: auto;
     position: relative;
     margin: 0;
+    overflow: hidden;
 }
 
 .device-mode-screen-area {
     position: absolute;
     left: 0;
     right: 0;
     width: 0;
     height: 0;
     background-color: #171717;
     box-shadow: hsl(0, 0%, 88%) 1px 1px 0 1px, hsla(0, 0%, 80%, 0.6) 0 0 16px;
@@ skipping 44 matching lines @@
 
 .device-mode-page-area {
     position: absolute;
     left: 0;
     right: 0;
     width: 0;
     height: 0;
     display: flex;
     background-color: #fcfcfc;
 }