Allow constructing aos::UUID from a span.

Change-Id: Ia676f0051841ffe2cc9441ef8aeed7a8f5bb0a85
Signed-off-by: James Kuszmaul <james.kuszmaul@bluerivertech.com>
diff --git a/aos/uuid.h b/aos/uuid.h
index b03e074..aabca37 100644
--- a/aos/uuid.h
+++ b/aos/uuid.h
@@ -37,6 +37,9 @@
   // transformation.
   static UUID FromVector(const flatbuffers::Vector<uint8_t> *data);
 
+  // Initializes new UUID from data.
+  static UUID FromSpan(absl::Span<const uint8_t> data);
+
   // Returns the boot UUID for the current linux computer.
   static UUID BootUUID();