Move mutex.h into base/mutex.h.

We don't actually need any hackery to get the right mutex.h any
more, but since we planned on having the google3-like stuff
in google3-like locations, this is an easy one to fix.

Change-Id: Ie27464ebbc208a6f4e694a97cf26b1cee0737009
diff --git a/src/jdwp/jdwp.h b/src/jdwp/jdwp.h
index fbca7d1..d8e5981 100644
--- a/src/jdwp/jdwp.h
+++ b/src/jdwp/jdwp.h
@@ -17,10 +17,10 @@
 #ifndef ART_JDWP_JDWP_H_
 #define ART_JDWP_JDWP_H_
 
+#include "base/mutex.h"
 #include "jdwp/jdwp_bits.h"
 #include "jdwp/jdwp_constants.h"
 #include "jdwp/jdwp_expand_buf.h"
-#include "../mutex.h" // TODO: fix our include path!
 
 #include <pthread.h>
 #include <stddef.h>