vp8e - boolcoder unit test

Adds a unit test to the boolcoder that tests encoding 
and decoding thousands of different bits, with different 
probabilities in different patterns.   

Code borrowed from the webp project - and its committers.

Change-Id: Icabbb884d57e666496490c961dd29b246144ab3e
diff --git a/vp8/vp8cx.mk b/vp8/vp8cx.mk
index b7f3494..e2557eb 100644
--- a/vp8/vp8cx.mk
+++ b/vp8/vp8cx.mk
@@ -87,6 +87,8 @@
 VP8_CX_SRCS-$(CONFIG_MULTI_RES_ENCODING) += encoder/mr_dissim.c
 VP8_CX_SRCS-$(CONFIG_MULTI_RES_ENCODING) += encoder/mr_dissim.h
 
+VP8_CX_SRCS-$(CONFIG_UNIT_TESTS) += encoder/boolcoder_test.cc
+
 ifeq ($(CONFIG_REALTIME_ONLY),yes)
 VP8_CX_SRCS_REMOVE-yes += encoder/firstpass.c
 VP8_CX_SRCS_REMOVE-yes += encoder/temporal_filter.c