Fix a crash in MimeHandlerServiceImpl::AbortStream().

extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc

Index: extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc
diff --git a/extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc b/extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc
index cb7b280d388870ca441e81c95bbbdbfd3ae46209..7003f7faaedf7dfc3f4c81ebd93825c031d0acb3 100644
--- a/extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc
+++ b/extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc
@@ -39,13 +39,14 @@ StreamContainer::StreamContainer(scoped_ptr<content::StreamInfo> stream,
       handler_url_(handler_url),
       extension_id_(extension_id),
       weak_factory_(this) {
+  DCHECK(stream_);
 }
 
 StreamContainer::~StreamContainer() {
 }
 
 void StreamContainer::Abort(const base::Closure& callback) {
-  if (!stream_) {
+  if (!stream_->handle) {
     callback.Run();
     return;
   }