Replace net-internals/export tab with deprecation msg and button to show old UI.

chrome/browser/resources/net_internals/export_view.html

 <style>
 
 #export-view-privacy-warning {
   border: 1px solid rgb(238, 0, 0);
   color: rgb(238, 0, 0);
   padding: 5px;
 }
 
 #export-view-save-log-file {
   font-size: 100%;
   font-weight: bold;
 }
 
 #export-view-user-comments {
   max-width: 100%;
 }
 
 </style>
 
 <div id=export-view-tab-content class=content-box>
-  <div>
+  <div id=export-view-deprecated-notice>
+    <b>WARNING</b>: chrome://net-internals is being deprecated for exporting log files (<a href="https://bugs.chromium.org/p/chromium/issues/detail?id=678386" target="_blank">crbug.com/678386</a>).
+    <p>
+      Use <a href="chrome://net-export" target="_blank">chrome://net-export</a> instead.
+    </p>
+    <button id=export-view-show-deprecated-ui>Show deprecated UI</button>
+  
+  </div>
+
+  <div style="display: none" id=export-view-ui-deprecated>
     <input id=export-view-privacy-stripping-checkbox type=checkbox checked=yes>
     <label for=export-view-privacy-stripping-checkbox>
       Strip private information (cookies and credentials).
     </label>
     <div id=export-view-privacy-warning style="display:none">
       <b>WARNING</b>: Events were captured while full byte logging was enabled.
       This means the dump may contain private information.
     </div>
 
     <div style='margin-top:10px; margin-bottom: 5px'>
       <textarea cols=50 rows=5 placeholder="Explain what went wrong here. (These notes will be included in the dump file. Be sure to mention the specific URLs, so investigators know what to look for!)" id=export-view-user-comments></textarea>
     </div>
     <button id=export-view-save-log-file>Save to file</button>
 
     <pre id=export-view-save-status-text></pre>
 
     <div style='margin-top: 10px; margin-left: 10px;'>
       <a href="https://sites.google.com/a/chromium.org/dev/for-testers/providing-network-details" target="_blank">
         How to provide data for bug reports
       </a>
     </div>
-
+  
   </div>
 
   <a style="display: none" id=export-view-download-anchor download="net-internals-log.json"></a>
 
 </div>