WebUI: Fix crash while loading scripts for webview.[add/remove]ContentScripts API.

extensions/browser/web_ui_user_script_loader.cc

 // 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.
 
 #include "extensions/browser/web_ui_user_script_loader.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/strings/string_util.h"
@@ skipping 68 matching lines @@
   for (const std::unique_ptr<extensions::UserScript>& script :
        *user_scripts_cache_) {
     if (added_script_ids.count(script->id()) == 0)
       continue;
 
     auto iter = script_render_info_map_.find(script->id());
     DCHECK(iter != script_render_info_map_.end());
     int render_process_id = iter->second.render_process_id;
     int render_frame_id = iter->second.render_frame_id;
 
-    content::BrowserContext* browser_context =
-        content::RenderProcessHost::FromID(render_process_id)
-            ->GetBrowserContext();
+    content::RenderProcessHost* render_process_host =
+        content::RenderProcessHost::FromID(render_process_id);
 
-    CreateWebUIURLFetchers(script->js_scripts(), browser_context,
-                           render_process_id, render_frame_id);
-    CreateWebUIURLFetchers(script->css_scripts(), browser_context,
-                           render_process_id, render_frame_id);
+    // LoadScripts may not be synchronous with AddScripts. Hence the
+    // |render_process_host| may no longer be alive. This should fix
+    // crbug.com/720331. TODO(karandeepb): Investigate if there are any side
+    // effects of the render process host no longer being alive and add a test.
+    if (render_process_host) {
+      content::BrowserContext* browser_context =
+          render_process_host->GetBrowserContext();
+
+      CreateWebUIURLFetchers(script->js_scripts(), browser_context,
+                             render_process_id, render_frame_id);
+      CreateWebUIURLFetchers(script->css_scripts(), browser_context,
+                             render_process_id, render_frame_id);
+    }
 
     script_render_info_map_.erase(script->id());
   }
 
   // If no fetch is needed, call OnWebUIURLFetchComplete directly.
   if (fetchers_.empty()) {
     OnWebUIURLFetchComplete();
     return;
   }
   for (const auto& fetcher : fetchers_)
@@ skipping 49 matching lines @@
 }
 
 void WebUIUserScriptLoader::OnWebUIURLFetchComplete() {
   content::BrowserThread::PostTask(
       content::BrowserThread::FILE, FROM_HERE,
       base::Bind(&SerializeOnFileThread, base::Passed(&user_scripts_cache_),
                  scripts_loaded_callback_));
   scripts_loaded_callback_.Reset();
   user_scripts_cache_.reset();
 }