Fix a crash in the FileSystem API when the app window closes during a call.

chrome/browser/extensions/api/file_system/file_system_api.cc

Index: chrome/browser/extensions/api/file_system/file_system_api.cc
diff --git a/chrome/browser/extensions/api/file_system/file_system_api.cc b/chrome/browser/extensions/api/file_system/file_system_api.cc
index a6e91cb30de3808c4a33d1f60025fa35fbdee455..dc10a6b4c35272adb2d58f3c4017b4246c51290e 100644
--- a/chrome/browser/extensions/api/file_system/file_system_api.cc
+++ b/chrome/browser/extensions/api/file_system/file_system_api.cc
@@ -339,6 +339,8 @@ void FileSystemEntryFunction::CheckWritableFiles(
 void FileSystemEntryFunction::RegisterFileSystemsAndSendResponse(
     const std::vector<base::FilePath>& paths) {
   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
+  if (!render_view_host_)
+    return;
 
   CreateResponse();
   for (std::vector<base::FilePath>::const_iterator it = paths.begin();