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

base/shared_memory_posix.cc

Index: base/shared_memory_posix.cc
diff --git a/base/shared_memory_posix.cc b/base/shared_memory_posix.cc
index 7283cbda42a40799148abe1cf099579b560939a4..ae814d732d6e444dace1425a6b8d2ef964909233 100644
--- a/base/shared_memory_posix.cc
+++ b/base/shared_memory_posix.cc
@@ -14,6 +14,7 @@
 #include "base/logging.h"
 #include "base/platform_thread.h"
 #include "base/safe_strerror_posix.h"
+#include "base/thread_restrictions.h"
 #include "base/utf_string_conversions.h"
 
 namespace base {
@@ -146,6 +147,11 @@ bool SharedMemory::CreateOrOpen(const std::string& name,
                                 int posix_flags, uint32 size) {
   DCHECK(mapped_file_ == -1);
 
+  // This function theoretically can block on the disk, but realistically
+  // the temporary files we create will just go into the buffer cache
+  // and be deleted before they ever make it out to disk.
+  base::ThreadRestrictions::ScopedAllowIO allow_io;
+
   file_util::ScopedFILE file_closer;
   FILE *fp;