GN: move webrtc/video/ targets from webrtc/BUILD.gn into webrtc/video/BUILD.gn

webrtc/test/BUILD.gn

Index: webrtc/test/BUILD.gn
diff --git a/webrtc/test/BUILD.gn b/webrtc/test/BUILD.gn
index 5a1e71aa9ab22a8c8b61bb32e431ba26aaf956b3..1b4bafd6ff869cfdb0e7e14075b1c4247c21984e 100644
--- a/webrtc/test/BUILD.gn
+++ b/webrtc/test/BUILD.gn
@@ -193,6 +193,18 @@ rtc_source_set("test_support_main_threaded_mac") {
   ]
 }
 
+rtc_source_set("run_test") {
+  testonly = true
+  sources = [
+    "run_test.h",
+  ]
+  if (is_mac) {
+    sources += [ "mac/run_test.mm" ]
+  } else {
+    sources += [ "run_test.cc" ]
+  }
+}
+
 test_support_unittests_resources = [
   "//resources/foreman_cif_short.yuv",
   "//resources/video_coding/frame-ethernet-ii.pcap",