Fsync directories after creating files

Bug: 120248692
Test: adb shell locksettings set-pin 1111 && \
    adb shell "echo b > /proc/sysrq-trigger"
Change-Id: I53d252942c21365983b4f8b6e0948b1864f195c1
diff --git a/Utils.h b/Utils.h
index 7976302..0b35a7b 100644
--- a/Utils.h
+++ b/Utils.h
@@ -131,6 +131,8 @@
 
 status_t WaitForFile(const char* filename, std::chrono::nanoseconds timeout);
 
+bool FsyncDirectory(const std::string& dirname);
+
 }  // namespace vold
 }  // namespace android