Make <media/MediaMetrics.h> safe to use directly

Previously, it assumed that the user had included other header files.
Now you can use it on its own, which is important for an API ("include
what you use").

Test: builds OK
Change-Id: Ib64eec20576dcf5a5dffe1ed670465cb590ef9e3

media/libmediametrics/include/media/MediaMetrics.h

@@ -24,6 +24,9 @@
 // for that string to the caller. The caller is responsible for calling free()
 // on that pointer when done using the value.
 
+#include <sys/cdefs.h>
+#include <sys/types.h>
+
 __BEGIN_DECLS
 
 // internally re-cast to the behind-the-scenes C++ class instance