Fix renderer crashes when frame gets detached while injectng user scripts.

chrome/renderer/extensions/user_script_slave.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/renderer/extensions/user_script_slave.h"
 
 #include <map>
 
 #include "base/command_line.h"
 #include "base/logging.h"
@@ skipping 332 matching lines @@
            iter != sources.end(); ++iter) {
         extensions_executing_scripts[extension->id()].insert(
             GURL(iter->url).path());
       }
     }
   }
 
   // Notify the browser if any extensions are now executing scripts.
   if (!extensions_executing_scripts.empty()) {
     blink::WebFrame* top_frame = frame->top();
-    content::RenderView* render_view =
-        content::RenderView::FromWebView(top_frame->view());
-    render_view->Send(new ExtensionHostMsg_ContentScriptsExecuting(
-        render_view->GetRoutingID(),
-        extensions_executing_scripts,
-        render_view->GetPageId(),
-        GetDataSourceURLForFrame(top_frame)));
+    if (top_frame) {

[dcheng, 2014/02/07 16:53:37]

top() should really never return 0... if you can wait until
https://codereview.chromium.org/156123004/ lands, that will be the case once
again.

+      content::RenderView* render_view =
+          content::RenderView::FromWebView(top_frame->view());
+      if (render_view) {
+        render_view->Send(new ExtensionHostMsg_ContentScriptsExecuting(
+            render_view->GetRoutingID(),
+            extensions_executing_scripts,
+            render_view->GetPageId(),
+            GetDataSourceURLForFrame(top_frame)));
+      }
+    }
   }
 
   // Log debug info.
   if (location == UserScript::DOCUMENT_START) {
     UMA_HISTOGRAM_COUNTS_100("Extensions.InjectStart_CssCount", num_css);
     UMA_HISTOGRAM_COUNTS_100("Extensions.InjectStart_ScriptCount", num_scripts);
     if (num_css || num_scripts)
       UMA_HISTOGRAM_TIMES("Extensions.InjectStart_Time", timer.Elapsed());
   } else if (location == UserScript::DOCUMENT_END) {
     UMA_HISTOGRAM_COUNTS_100("Extensions.InjectEnd_ScriptCount", num_scripts);
     if (num_scripts)
       UMA_HISTOGRAM_TIMES("Extensions.InjectEnd_Time", timer.Elapsed());
   } else if (location == UserScript::DOCUMENT_IDLE) {
     UMA_HISTOGRAM_COUNTS_100("Extensions.InjectIdle_ScriptCount", num_scripts);
     if (num_scripts)
       UMA_HISTOGRAM_TIMES("Extensions.InjectIdle_Time", timer.Elapsed());
   } else {
     NOTREACHED();
   }
 }
 
 }  // namespace extensions