Pass self to lock methods.

This avoids frequent recomputation of
Thread::Current/pthread_getspecific.

Also add a futex based reader/writer mutex that is disabled.

Change-Id: I118fdb99ef1d1c4bfda6446ba3a0d8b6ab31eaee
diff --git a/build/Android.common.mk b/build/Android.common.mk
index c5e45e3..78743a7 100644
--- a/build/Android.common.mk
+++ b/build/Android.common.mk
@@ -196,6 +196,7 @@
 	src/jdwp/jdwp_socket.cc \
 	src/jni_internal.cc \
 	src/jobject_comparator.cc \
+	src/locks.cc \
 	src/logging.cc \
 	src/mark_stack.cc \
 	src/mark_sweep.cc \
@@ -378,6 +379,7 @@
 	src/invoke_type.h \
 	src/jdwp/jdwp.h \
 	src/jdwp/jdwp_constants.h \
+	src/locks.h \
 	src/mutex.h \
 	src/object.h \
 	src/thread.h \