Add flock(2)ing on dex-cache files to prevent races

Bug: 9071417
Change-Id: I1ee9ff281867f90fba7a8ed8bbf06b33ac29d511
diff --git a/runtime/output_stream_test.cc b/runtime/output_stream_test.cc
index c9e0ede..8da2ac9 100644
--- a/runtime/output_stream_test.cc
+++ b/runtime/output_stream_test.cc
@@ -62,7 +62,7 @@
   FileOutputStream output_stream(tmp.GetFile());
   SetOutputStream(output_stream);
   GenerateTestOutput();
-  UniquePtr<File> in(OS::OpenFile(tmp.GetFilename().c_str(), false));
+  UniquePtr<File> in(OS::OpenFileForReading(tmp.GetFilename().c_str()));
   EXPECT_TRUE(in.get() != NULL);
   std::vector<uint8_t> actual(in->GetLength());
   bool readSuccess = in->ReadFully(&actual[0], actual.size());