Fix compiler error in vp8/9 decoder test

The test file compiler fails if one uses --disable-vp8-decoder
--enable-vp9-decoder. It effectively turns on CONFIG_VP8 and
CONFIG_DECODERS, but turns off CONFIG_VP8_DECODER, which causes
compiler error at test_vector_test.cc.

This commit fixes this issue by adding vp8/9 decoder flags to
the decoder behavior test, respectively.

Change-Id: I097ff8fd5e12715a94a565a82e54503885eb7187

test/test_vector_test.cc

@@ -135,6 +135,7 @@ TEST_P(TestVectorTest, MD5Match) {
 
 // Test VP8 decode in serial mode with single thread.
 // NOTE: VP8 only support serial mode.
+#if CONFIG_VP8_DECODER
 VP8_INSTANTIATE_TEST_CASE(
     TestVectorTest,
     ::testing::Combine(
@@ -143,8 +144,10 @@ VP8_INSTANTIATE_TEST_CASE(
         ::testing::ValuesIn(libvpx_test::kVP8TestVectors,
                             libvpx_test::kVP8TestVectors +
                                 libvpx_test::kNumVP8TestVectors)));
+#endif  // CONFIG_VP8_DECODER
 
 // Test VP9 decode in serial mode with single thread.
+#if CONFIG_VP9_DECODER
 VP9_INSTANTIATE_TEST_CASE(
     TestVectorTest,
     ::testing::Combine(
@@ -154,8 +157,6 @@ VP9_INSTANTIATE_TEST_CASE(
                             libvpx_test::kVP9TestVectors +
                                 libvpx_test::kNumVP9TestVectors)));
 
-
-#if CONFIG_VP9_DECODER
 // Test VP9 decode in frame parallel mode with different number of threads.
 INSTANTIATE_TEST_CASE_P(
     VP9MultiThreadedFrameParallel, TestVectorTest,