Fix color space bug in wrapper of H264 decoder

Bug: none
Change-Id: I8309e5e3c177ae75712fa257e083ea2018a1f8e2
Reviewed-on: https://webrtc-review.googlesource.com/c/121760
Commit-Queue: Johannes Kron <kron@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26597}

modules/video_coding/BUILD.gn

@@ -760,6 +760,10 @@ if (rtc_include_tests) {
 
   rtc_source_set("video_coding_modules_tests") {
     testonly = true
+    defines = []
+    if (rtc_use_h264) {
+      defines += [ "WEBRTC_USE_H264" ]
+    }
 
     sources = [
       "codecs/h264/test/h264_impl_unittest.cc",