Use Jsmn to parse json data

[ Merge of http://go/wvgerrit/16628 ]

Jsmn will replace a local method that parsed json init data.
Added a fix to include all key Ids in the WidevineCencHeader rather than
just the first. Also modified the content_id to reflect that it is a
base64 encoded value.

b/20630275

Change-Id: I7080c8cea21be4dea09a4905a96b4cc03e584c1d

libwvdrmengine/mediadrm/test/Android.mk

@@ -21,9 +21,10 @@ LOCAL_STATIC_LIBRARIES := \
   libcdm_protos \
   libcdm_utils \
   libcrypto_static \
+  libjsmn \
+  libgtest \
   libwvgmock \
   libwvgmock_main \
-  libgtest \
   libwvlevel3 \
   libwvdrmdrmplugin \