Fix issue with DOM Distiller viewer when renderer goes away.

components/dom_distiller/content/dom_distiller_viewer_source.cc

 // Copyright 2014 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 "components/dom_distiller/content/dom_distiller_viewer_source.h"
 
 #include <sstream>
 #include <string>
 #include <vector>
 
@@ skipping 250 matching lines @@
   return scheme_ + "://";
 }
 
 void DomDistillerViewerSource::StartDataRequest(
     const std::string& path,
     int render_process_id,
     int render_frame_id,
     const content::URLDataSource::GotDataCallback& callback) {
   content::RenderFrameHost* render_frame_host =
       content::RenderFrameHost::FromID(render_process_id, render_frame_id);
-  DCHECK(render_frame_host);
+  if (!render_frame_host) return;
   content::RenderViewHost* render_view_host =
       render_frame_host->GetRenderViewHost();
   DCHECK(render_view_host);
   CHECK_EQ(0, render_view_host->GetEnabledBindings());
 
   if (kViewerCssPath == path) {
     std::string css = viewer::GetCss();
     callback.Run(base::RefCountedString::TakeString(&css));
     return;
   }
   if (kViewerJsPath == path) {
     std::string js = viewer::GetJavaScript();
     callback.Run(base::RefCountedString::TakeString(&js));
     return;
   }
   if (kViewerViewOriginalPath == path) {
     content::RecordAction(base::UserMetricsAction("DomDistiller_ViewOriginal"));
     callback.Run(NULL);
     return;
   }
   content::WebContents* web_contents =
-      content::WebContents::FromRenderFrameHost(
-          content::RenderFrameHost::FromID(render_process_id,
-                                           render_frame_id));
+      content::WebContents::FromRenderFrameHost(render_frame_host);
   DCHECK(web_contents);
   // An empty |path| is invalid, but guard against it. If not empty, assume
   // |path| starts with '?', which is stripped away.
   const std::string path_after_query_separator =
       path.size() > 0 ? path.substr(1) : "";
   RequestViewerHandle* request_viewer_handle = new RequestViewerHandle(
       web_contents, scheme_, path_after_query_separator, callback,
       dom_distiller_service_->GetDistilledPagePrefs());
   scoped_ptr<ViewerHandle> viewer_handle = viewer::CreateViewRequest(
       dom_distiller_service_, path, request_viewer_handle,
@@ skipping 38 matching lines @@
     const net::URLRequest* request,
     std::string* path) const {
 }
 
 std::string DomDistillerViewerSource::GetContentSecurityPolicyObjectSrc()
     const {
   return "object-src 'none'; style-src 'self' https://fonts.googleapis.com;";
 }
 
 }  // namespace dom_distiller