Add Mock OEMCrypto Stub

I added a Mock OEMCrypto implementation with stubs only.

I corrected the "extern C" location in OEMCrypto.h. (Thanks, Jerry!)

I added some Android.mk files that allows us to compile and
run a few simple unit tests.

Unit Test 1: The library compiles. (passes)
Unit Test 2: The test program links and runs. (passes)

Change-Id: Ib4c9554553de49645b5841b0bae889728cbfc8b1

libwvdrmengine/oemcrypto/mock/Android.mk

@@ -0,0 +1,20 @@
+LOCAL_PATH:= $(call my-dir)
+
+include $(CLEAR_VARS)
+
+
+LOCAL_SRC_FILES := MockOEMCrypto.cpp
+LOCAL_C_INCLUDES += vendor/widevine/libwvdrmengine/oemcrypto/include
+
+LOCAL_MODULE := libMockOEMCrypto
+
+LOCAL_MODULE_CLASS := SHARED_LIBRARIES
+LOCAL_MODULE_SUFFIX := .so
+
+LOCAL_MODULE_TAGS := tests
+
+LOCAL_SHARED_LIBRARIES := \
+    liblog \
+    libutils \
+
+include $(BUILD_SHARED_LIBRARY)