Reland of Enabling `gn check` on webrtc/test

webrtc/modules/rtp_rtcp/BUILD.gn

Index: webrtc/modules/rtp_rtcp/BUILD.gn
diff --git a/webrtc/modules/rtp_rtcp/BUILD.gn b/webrtc/modules/rtp_rtcp/BUILD.gn
index 7f2d64fe5342aa62743d34a355a831e275073e3b..a9e257ef6aa2c0ffabde264134266059ddbb2017 100644
--- a/webrtc/modules/rtp_rtcp/BUILD.gn
+++ b/webrtc/modules/rtp_rtcp/BUILD.gn
@@ -211,6 +211,21 @@ rtc_source_set("fec_test_helper") {
   }
 }
 
+rtc_source_set("mock_rtp_rtcp") {
+  testonly = true
+  sources = [
+    "mocks/mock_recovered_packet_receiver.h",
+    "mocks/mock_rtcp_rtt_stats.h",
+    "mocks/mock_rtp_rtcp.h",
+  ]
+  deps = [
+    ":rtp_rtcp",
+    "..:module_api",
+    "../../base:rtc_base_approved",
+    "../../test:test_support",
+  ]
+}
+
 if (rtc_include_tests) {
   rtc_executable("test_packet_masks_metrics") {
     testonly = true
@@ -250,21 +265,6 @@ if (rtc_include_tests) {
     }
   }
 
-  rtc_source_set("mock_rtp_rtcp") {
-    testonly = true
-    sources = [
-      "mocks/mock_recovered_packet_receiver.h",
-      "mocks/mock_rtcp_rtt_stats.h",
-      "mocks/mock_rtp_rtcp.h",
-    ]
-    deps = [
-      ":rtp_rtcp",
-      "..:module_api",
-      "../../base:rtc_base_approved",
-      "../../test:test_support",
-    ]
-  }
-
   rtc_source_set("rtp_rtcp_unittests") {
     testonly = true