Enable tests using WebM files only if webm_io is enabled

There are a few tests which read/write directly to/from WebM files. They should
be disabled when --disable-webm-io is passed.

Change-Id: Ibac4732e27c66da33082151ba6e6993eaa9a1efd
diff --git a/test/test.mk b/test/test.mk
index f1a8ed9..a489e63 100644
--- a/test/test.mk
+++ b/test/test.mk
@@ -42,6 +42,7 @@
 LIBVPX_TEST_SRCS-yes                   += encode_test_driver.h
 
 ## WebM Parsing
+ifeq ($(CONFIG_WEBM_IO), yes)
 NESTEGG_SRCS                           += ../third_party/nestegg/halloc/halloc.h
 NESTEGG_SRCS                           += ../third_party/nestegg/halloc/src/align.h
 NESTEGG_SRCS                           += ../third_party/nestegg/halloc/src/halloc.c
@@ -53,11 +54,14 @@
 LIBVPX_TEST_SRCS-$(CONFIG_DECODERS)    += ../webmdec.c
 LIBVPX_TEST_SRCS-$(CONFIG_DECODERS)    += ../webmdec.h
 LIBVPX_TEST_SRCS-$(CONFIG_DECODERS)    += webm_video_source.h
+endif
 
 LIBVPX_TEST_SRCS-$(CONFIG_DECODERS)    += test_vector_test.cc
 
-# Currently we only support decoder perf tests for vp9
-ifeq ($(CONFIG_DECODE_PERF_TESTS)$(CONFIG_VP9_DECODER), yesyes)
+# Currently we only support decoder perf tests for vp9. Also they read from WebM
+# files, so WebM IO is required.
+ifeq ($(CONFIG_DECODE_PERF_TESTS)$(CONFIG_VP9_DECODER)$(CONFIG_WEBM_IO), \
+      yesyesyes)
 LIBVPX_TEST_SRCS-yes                   += decode_perf_test.cc
 endif