[DevTools] Make UI.GlassPane position contentElement for different overlay controls.

third_party/WebKit/Source/devtools/front_end/ui/dialog.css

 /*
  * Copyright (c) 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 {
-    position: absolute;
-    box-shadow: 0 0 0 1px rgba(0, 0, 0, 0.2),
-                0 2px 4px rgba(0, 0, 0, 0.2),
-                0 2px 6px rgba(0, 0, 0, 0.1);
+    box-shadow: 0 0 0 1px rgba(0, 0, 0, 0.2), 0 2px 4px rgba(0, 0, 0, 0.2), 0 2px 6px rgba(0, 0, 0, 0.1);
     background: white;
     justify-content: flex-start;
     align-items: stretch;
 }
 
 .widget {
     display: flex;
     flex: auto;
     justify-content: flex-start;
     align-items: stretch;
 }
 
 :host-context(.wraps-content) {
-    justify-content: center;
     align-items: flex-start;
     overflow: hidden;
 }
 
 :host-context(.wraps-content) .widget {
     flex: none !important;
-    justify-content: center;
     align-items: center;
 }
 
 .dialog-close-button {
     position: absolute;
     right: 9px;
     top: 9px;
 }