Ensure that in-process plugins can't destroy themselves by closing a URLLoader

content/renderer/pepper/pepper_url_loader_host.cc

Index: content/renderer/pepper/pepper_url_loader_host.cc
diff --git a/content/renderer/pepper/pepper_url_loader_host.cc b/content/renderer/pepper/pepper_url_loader_host.cc
index 27d427149eb1b45a38f3fefba1d4fec459ade0d5..4e505a9d5a12ba2674b13a4ba79e05a5d8ada308 100644
--- a/content/renderer/pepper/pepper_url_loader_host.cc
+++ b/content/renderer/pepper/pepper_url_loader_host.cc
@@ -361,8 +361,11 @@ void PepperURLLoaderHost::SendOrderedUpdateToPlugin(IPC::Message* message) {
 void PepperURLLoaderHost::Close() {
   if (loader_.get())
     loader_->cancel();
-  else if (main_document_loader_)
-    GetFrame()->stopLoading();
+  else if (main_document_loader_) {
+    blink::WebFrame* frame = GetFrame();
+    if (frame)
+      frame->stopLoading();
+  }
 }
 
 blink::WebLocalFrame* PepperURLLoaderHost::GetFrame() {