Extract Session class from oemcrypto_test.

This allows the OEMCrypto session state to be accessed by
tests in other modules.  For example, keys can be added for testing
encryption and decryption operations in CDM-level tests.

Merge from Widevine repo of http://go/wvgerrit/18127,
http://go/wvgerrit/18591, http://go/wvgerrit/18581 and
http://go/wvgerrit/20802.

Change-Id: Ie0d071a2da610c0856ae6356a0abf054013a1b87

libwvdrmengine/oemcrypto/test/common.mk

@@ -6,6 +6,8 @@ LOCAL_LDFLAGS+=-Wl,--hash-style=both
 endif
 
 LOCAL_SRC_FILES:= \
+  oec_device_features.cpp \
+  oec_session_util.cpp \
   oemcrypto_test.cpp \
   oemcrypto_test_android.cpp \
   oemcrypto_test_main.cpp \