altref_test: move AltRefTest instantiation w/in VP8 check

some configurations may fail if AltRefTest is undefined though
VP8_INSTANTIATE_TEST_CASE is defined away.

Change-Id: I7272775a506718336bd6cee2225cf83bd72fede5

test/altref_test.cc

@@ -65,6 +65,9 @@ TEST_P(AltRefTest, MonotonicTimestamps) {
   EXPECT_GE(altref_count(), 1);
 }
 
+VP8_INSTANTIATE_TEST_CASE(AltRefTest,
+                          ::testing::Range(kLookAheadMin, kLookAheadMax));
+
 #endif  // CONFIG_VP8_ENCODER
 
 class AltRefForcedKeyTest
@@ -149,9 +152,6 @@ TEST_P(AltRefForcedKeyTest, ForcedFrameIsKey) {
   }
 }
 
-VP8_INSTANTIATE_TEST_CASE(AltRefTest,
-                          ::testing::Range(kLookAheadMin, kLookAheadMax));
-
 VP8_INSTANTIATE_TEST_CASE(
     AltRefForcedKeyTest,
     ::testing::Values(::libvpx_test::kOnePassGood),