[MD settings] OnStartup settings layout closer to mocks

chrome/browser/resources/settings/settings_dialog.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. */
 
 /**
  * @fileoverview
  * Common dialog styles for Material Design settings.
  */
 
 #dialog-content {
@@ skipping 10 matching lines @@
   padding-bottom: 5px;
   padding-top: 5px;
 }
 
 paper-dialog .title {
   flex: 1;
   font-size: 1.13em;
 }
 
 paper-dialog .body {
+  display: flex;
+  flex-flow: column;
   font-size: 1em;
   margin: 20px 0;
 }
 
 paper-dialog .title,
 paper-dialog .body {
   -webkit-padding-end: 24px;
   -webkit-padding-start: 24px;
 }
 
 paper-dialog .action-button {
   -webkit-margin-start: 10px;
   background-color: rgb(66, 133, 244);
   color: white;
   font-weight: 500;
 }
 
 paper-dialog .cancel-button {
   color: rgb(109, 109, 109);
   font-weight: 500;
 }
 
 paper-dialog .explanation {
+  flex: 1;

[dpapad, 2016/01/12 00:43:47]

As discussed in person, it looks better to me to remove the flex:1 from here and
also remove the min-height from the "Add a page" dialog.

[dschuyler, 2016/01/12 19:49:37]

I like those suggestions.  I've asked Alan for his thoughts.
I'm going to make these changes for now and make adjustments
later if Alan would like the layout done differently. 

   margin-bottom: 35px;
 }
 
 paper-dialog .button-container {
   display: flex;
-  flex: 1;
   justify-content: flex-end;
 }
 
 paper-dialog paper-button {
   margin: 0;
   min-width: auto;
 }
 
 paper-dialog paper-button[toggles][active] {
   background-color: LightGray;
 }