media/gpu VEA unittest: Enable kVaapiVp9Encoder on VEA unittest

The former way to enable kVaapiVp9Encoder in VEA unittest is wrong. It enables
kVaapiVp9Encoder in the begging of main() function in the test. Features are
overwritten later by base::TestSuite::Initialize(). Furthermore, it is too late
if the feature is enabled in each test case. base::TestSuite::Initialize()
queries the driver and the obtained capabilities will be used in the test case.
Hence, we have to enable kVaapiVp9Encoder between base::TestSuite::Initialize()
and media::VaapiWrapper::PreSandboxInitialization().

Bug: 811912, 930532
Test: VEA unittest with VP9 stream
Change-Id: Id1601d5ce985c189820f380df5c2e23ea265e17c
Reviewed-on: https://chromium-review.googlesource.com/c/1490987
Commit-Queue: Hirokazu Honda <hiroh@chromium.org>
Commit-Queue: Pawel Osciak <posciak@chromium.org>
Auto-Submit: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Pawel Osciak <posciak@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635945}

media/gpu/video_encode_accelerator_unittest.cc

@@ -2915,6 +2915,9 @@ class VEATestSuite : public base::TestSuite {
                     media::g_verify_all_output)));
 
 #if BUILDFLAG(USE_VAAPI)
+    base::test::ScopedFeatureList scoped_feature_list;
+    // TODO(crbug.com/811912): remove once enabled by default.
+    scoped_feature_list.InitAndEnableFeature(media::kVaapiVP9Encoder);
     media::VaapiWrapper::PreSandboxInitialization();
 #elif defined(OS_WIN)
     media::MediaFoundationVideoEncodeAccelerator::PreSandboxInitialization();
@@ -2937,12 +2940,6 @@ int main(int argc, char** argv) {
   mojo::core::Init();
   media::VEATestSuite test_suite(argc, argv);
 
-#if BUILDFLAG(USE_VAAPI)
-  base::test::ScopedFeatureList scoped_feature_list;
-  // TODO(crbug.com/811912): remove once enabled by default.
-  scoped_feature_list.InitAndEnableFeature(media::kVaapiVP9Encoder);
-#endif
-
   base::ShadowingAtExitManager at_exit_manager;
 
   // Needed to enable DVLOG through --vmodule.