WebUI: Don't check for removed download files when render process is gone

This blocks the history service shutdown.
The issue was originally introduced in https://codereview.chromium.org/1960223002
However, when render process is gone, there is no need to check removed files.
We can do that next time when downloads page is loaded

BUG=477975

Change-Id: I468cabc7d4c564591dfeaf4b0af66290e1ac8f53
Reviewed-on: https://chromium-review.googlesource.com/810107
Commit-Queue: Min Qin(OOO 12/7-1/10) <qinmin@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522207}

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

@@ -75,8 +75,7 @@ void CountDownloadsDOMEvents(DownloadsDOMEvent event) {
 
 MdDownloadsDOMHandler::MdDownloadsDOMHandler(
     content::DownloadManager* download_manager, content::WebUI* web_ui)
-    : list_tracker_(download_manager, web_ui),
-      weak_ptr_factory_(this) {
+    : list_tracker_(download_manager, web_ui) {
   // Create our fileicon data source.
   profile_ = Profile::FromBrowserContext(download_manager->GetBrowserContext());
   content::URLDataSource::Add(profile_, new FileIconSource());
@@ -139,12 +138,14 @@ void MdDownloadsDOMHandler::RegisterMessages() {
 void MdDownloadsDOMHandler::OnJavascriptDisallowed() {
   list_tracker_.Stop();
   list_tracker_.Reset();
-  CheckForRemovedFiles();
+  if (!render_process_gone_)
+    CheckForRemovedFiles();
 }
 
 void MdDownloadsDOMHandler::RenderProcessGone(base::TerminationStatus status) {
   // TODO(dbeam): WebUI + WebUIMessageHandler should do this automatically.
   // http://crbug.com/610450
+  render_process_gone_ = true;
   DisallowJavascript();
 }
 

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

@@ -153,9 +153,12 @@ class MdDownloadsDOMHandler : public content::WebContentsObserver,
   std::vector<IdSet> removals_;
 
   // User profile that corresponds to this handler.
-  Profile* profile_;
+  Profile* profile_ = nullptr;
 
-  base::WeakPtrFactory<MdDownloadsDOMHandler> weak_ptr_factory_;
+  // Whether the render process has gone.
+  bool render_process_gone_ = false;
+
+  base::WeakPtrFactory<MdDownloadsDOMHandler> weak_ptr_factory_{this};
 
   DISALLOW_COPY_AND_ASSIGN(MdDownloadsDOMHandler);
 };