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

chrome/renderer/extensions/user_script_slave.cc

Index: chrome/renderer/extensions/user_script_slave.cc
diff --git a/chrome/renderer/extensions/user_script_slave.cc b/chrome/renderer/extensions/user_script_slave.cc
index e45d490a1373b1ad6994df3176232b45b6784b8c..b8d4dc255f14ff2418325b696ae3d2f3a226fad7 100644
--- a/chrome/renderer/extensions/user_script_slave.cc
+++ b/chrome/renderer/extensions/user_script_slave.cc
@@ -350,13 +350,17 @@ void UserScriptSlave::InjectScripts(WebFrame* frame,
   // 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.