Require specific support for vaapi image codecs

Enable buildflag USE_VAAPI_IMAGE_CODECS when we're not on linux and
still using vaapi.

Change-Id: Id46698262b81c262a8b92636d0373cba4ebb5b99
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2441959
Commit-Queue: Ted Meyer <tmathmeyer@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816381}

components/viz/service/gl/gpu_service_impl.cc

@@ -394,10 +394,10 @@ GpuServiceImpl::GpuServiceImpl(
   }
 #endif
 
-#if BUILDFLAG(USE_VAAPI)
+#if BUILDFLAG(USE_VAAPI_IMAGE_CODECS)
   image_decode_accelerator_worker_ =
       media::VaapiImageDecodeAcceleratorWorker::Create();
-#endif
+#endif  // BUILDFLAG(USE_VAAPI_IMAGE_CODECS)
 
 #if defined(OS_APPLE)
   if (gpu_feature_info_.status_values[gpu::GPU_FEATURE_TYPE_METAL] ==

media/gpu/BUILD.gn

@@ -16,6 +16,7 @@ buildflag_header("buildflags") {
 
   flags = [
     "USE_VAAPI=$use_vaapi",
+    "USE_VAAPI_IMAGE_CODECS=$use_vaapi_image_codecs",
     "USE_V4L2_CODEC=$use_v4l2_codec",
     "USE_LIBV4L2=$use_v4lplugin",
   ]

media/gpu/args.gni

@@ -23,3 +23,11 @@ declare_args() {
   # encrypted content with HW video decoders.
   use_chromeos_protected_media = false
 }
+
+# GN requires args that depend on other args to be declared in successive
+# declare_args() blocks.
+declare_args() {
+  # VA-API also allows decoding of images, but we don't want to use this
+  # outside of chromeos, even if video decoding is enabled.
+  use_vaapi_image_codecs = use_vaapi && is_chromeos
+}