Thread IO safety: file_util annotated, IO thread blocked from doing IO

net/url_request/url_request_file_job.cc

Index: net/url_request/url_request_file_job.cc
diff --git a/net/url_request/url_request_file_job.cc b/net/url_request/url_request_file_job.cc
index 8c282ffb231425981a5ac21ff49ec96d9ff2c438..f9c6559065022a43e9e018c1356af2ef499876e0 100644
--- a/net/url_request/url_request_file_job.cc
+++ b/net/url_request/url_request_file_job.cc
@@ -23,6 +23,7 @@
 #include "base/message_loop.h"
 #include "base/platform_file.h"
 #include "base/string_util.h"
+#include "base/thread_restrictions.h"
 #include "build/build_config.h"
 #include "googleurl/src/gurl.h"
 #include "net/base/io_buffer.h"
@@ -128,8 +129,15 @@ void URLRequestFileJob::Start() {
     return;
   }
 #endif
+
+  // URL requests should not block on the disk!
+  //   http://code.google.com/p/chromium/issues/detail?id=59849
+  bool exists;
   base::PlatformFileInfo file_info;
-  bool exists = file_util::GetFileInfo(file_path_, &file_info);
+  {
+    base::ThreadRestrictions::ScopedAllowIO allow_io;
+    exists = file_util::GetFileInfo(file_path_, &file_info);
+  }
 
   // Continue asynchronously.
   MessageLoop::current()->PostTask(FROM_HERE, NewRunnableMethod(