[DevTools] Option to show device frames in emulation mode

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 34 matching lines @@
 .device-mode-media-container {
     flex: none;
     overflow: hidden;
     box-shadow: inset 0 -1px #ccc;
 }
 
 .device-mode-content-clip:not(.device-mode-rulers-visible) .device-mode-media-container {
     margin-bottom: 20px;
 }
 
+.device-mode-content-clip:not(.device-mode-frame-visible) .device-mode-outline-area {
+    visibility: hidden;
+}
+
 .device-mode-presets-container {
     flex: 0 0 20px;
     display: flex;
 }
 
 .device-mode-presets-container-inner {
     flex: auto;
     justify-content: center;
     position: relative;
     background-color: hsl(0, 0%, 90%);
@@ skipping 51 matching lines @@
 }
 
 .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;
+    z-index: 2;

[dgozman, 2016/02/01 17:18:27]

I'd prefer to avoid z-index. Can we instead rearrange things in the DOM?

[mmccoy, 2016/02/10 20:06:34]

Done!

+}
+
+.device-mode-screen-area {
+    width: 454px;
+    height: 921px;
 }
 
 .device-mode-screen-image {
     position: absolute;
     left: 0;
     top: 0;
     width: 100%;
     height: 100%;
 }
 
+.device-mode-outline-area {
+    position: absolute;
+    left: 0;
+    right: 0;
+    width: 0;
+    height: 0;
+    z-index: 1;
+}
+
+.device-mode-outline-image {
+    position: absolute;
+    left: 0;
+    top: 0;
+    width: 100%;
+    height: 100%;
+}
+
 .device-mode-resizer {
     position: absolute;
     display: flex;
     align-items: center;
     justify-content: center;
     overflow: hidden;
     transition: background-color 0.1s ease;
 }
 
 .device-mode-resizer:hover {
@@ skipping 140 matching lines @@
 .device-mode-ruler-top .device-mode-ruler-text {
     left: 2px;
     top: -2px;
 }
 
 .device-mode-ruler-left .device-mode-ruler-text {
     left: -4px;
     top: -15px;
     transform: rotate(270deg);
 }