Add RingBuffer class and test.

Change-Id: I63f66d70ccf43b5c3b49046cdfecf558ddbd6af7
diff --git a/aos/common/BUILD b/aos/common/BUILD
index 658a2e6..f4b57d5 100644
--- a/aos/common/BUILD
+++ b/aos/common/BUILD
@@ -393,3 +393,21 @@
     '//aos/common/util:death_test_log_implementation',
   ],
 )
+
+cc_library(
+  name = 'ring_buffer',
+  hdrs = [
+    'ring_buffer.h',
+  ],
+)
+
+cc_test(
+  name = 'ring_buffer_test',
+  srcs = [
+    'ring_buffer_test.cc',
+  ],
+  deps = [
+    ':ring_buffer',
+    '//aos/testing:googletest',
+  ],
+)