Simplify the implementation of ANGLE_INSTANTIATE_TEST

I mistakenly submitted a refactor with +2 but not +1 so a comment wasn't
addressed, hopefully fixes it.

BUG=angleproject:892

Change-Id: I096c2424449be196dfa949cc6ef662b766036330
Reviewed-on: https://chromium-review.googlesource.com/272905
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>

src/tests/test_utils/angle_test_instantiate.h

@@ -19,7 +19,7 @@ namespace angle
 // internally it T::getRenderer() const that should be implemented for test
 // parameter types.
 template <typename T>
-inline std::vector<T> FilterTestParams(const T *params, size_t numParams)
+std::vector<T> FilterTestParams(const T *params, size_t numParams)
 {
     std::vector<T> filtered;
 
@@ -59,21 +59,10 @@ inline std::vector<T> FilterTestParams(const T *params, size_t numParams)
     return filtered;
 }
 
-namespace detail {
-
-// Used with decltype to get the type of the first argument.
-template <typename T, typename ... Args>
-T ReturnFirst(T first, Args...)
-{
-    return first;
-}
-
-} // namespace detail
-
 // Instantiate the test once for each extra argument. The types of all the
 // arguments must match, and getRenderer must be implemented for that type.
-#define ANGLE_INSTANTIATE_TEST(testName, ...) \
-    const decltype(::angle::detail::ReturnFirst(__VA_ARGS__)) testName##params[] = {__VA_ARGS__}; \
+#define ANGLE_INSTANTIATE_TEST(testName, firstParam, ...) \
+    const decltype(firstParam) testName##params[] = { firstParam, ##__VA_ARGS__ }; \
     INSTANTIATE_TEST_CASE_P(, testName, testing::ValuesIn(::angle::FilterTestParams(testName##params, ArraySize(testName##params))));
 
 } // namespace angle