WebUI: Add JavaScript lifecycle-control to WebUIMessageHandler.

chrome/browser/ui/webui/md_downloads/md_downloads_dom_handler.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/ui/webui/md_downloads/md_downloads_dom_handler.h"
 
 #include <algorithm>
 #include <functional>
 
 #include "base/bind.h"
@@ skipping 115 matching lines @@
       base::Bind(&MdDownloadsDOMHandler::HandleCancel,
                  weak_ptr_factory_.GetWeakPtr()));
   web_ui()->RegisterMessageCallback("clearAll",
       base::Bind(&MdDownloadsDOMHandler::HandleClearAll,
                  weak_ptr_factory_.GetWeakPtr()));
   web_ui()->RegisterMessageCallback("openDownloadsFolder",
       base::Bind(&MdDownloadsDOMHandler::HandleOpenDownloadsFolder,
                  weak_ptr_factory_.GetWeakPtr()));
 }
 
-void MdDownloadsDOMHandler::RenderViewReused() {
+void MdDownloadsDOMHandler::OnJavascriptAllowed() {
+  list_tracker_.StartAndSendChunk();
+}
+
+void MdDownloadsDOMHandler::OnJavascriptDisallowed() {
   list_tracker_.Stop();
   list_tracker_.Reset();
   CheckForRemovedFiles();

[Dan Beam, 2016/04/18 23:13:20]

technically we want to check for removed files on *refresh*.

what are the chances that refresh and disallowing javascript diverge eventually?

[tommycli, 2016/04/19 17:45:37]

Hmm... I would imagine OnJavascriptDisallowed to being a superset of
OnRenderViewReused.

A Refresh should ALWAYS trigger a OnJavascriptDisallowed. Additionally, a
'Polymer element detached' should probably also trigger a DisallowJavascript
(currently non-existent) call.

 }
 
 void MdDownloadsDOMHandler::HandleGetDownloads(const base::ListValue* args) {
   CountDownloadsDOMEvents(DOWNLOADS_DOM_EVENT_GET_DOWNLOADS);
 
   bool terms_changed = list_tracker_.SetSearchTerms(*args);
   if (terms_changed)
     list_tracker_.Reset();
 
-  list_tracker_.StartAndSendChunk();
+  AllowJavascript();
 }
 
 void MdDownloadsDOMHandler::HandleOpenFile(const base::ListValue* args) {
   CountDownloadsDOMEvents(DOWNLOADS_DOM_EVENT_OPEN_FILE);
   content::DownloadItem* file = GetDownloadByValue(args);
   if (file)
     file->OpenDownload();
 }
 
 void MdDownloadsDOMHandler::HandleDrag(const base::ListValue* args) {
@@ skipping 250 matching lines @@
 content::WebContents* MdDownloadsDOMHandler::GetWebUIWebContents() {
   return web_ui()->GetWebContents();
 }
 
 void MdDownloadsDOMHandler::CheckForRemovedFiles() {
   if (GetMainNotifierManager())
     GetMainNotifierManager()->CheckForHistoryFilesRemoval();
   if (GetOriginalNotifierManager())
     GetOriginalNotifierManager()->CheckForHistoryFilesRemoval();
 }