Add video_loopback to gn.

webrtc/BUILD.gn

Index: webrtc/BUILD.gn
diff --git a/webrtc/BUILD.gn b/webrtc/BUILD.gn
index 94ce0120b61e73b84d076c385625bc51fcc17862..5ba2b75212e12a7b7c6d40dd5afd6e5f7ceec06a 100644
--- a/webrtc/BUILD.gn
+++ b/webrtc/BUILD.gn
@@ -294,6 +294,35 @@ if (!build_with_chromium) {
       "test",
     ]
   }
+
+  executable("video_loopback") {
+    testonly = true
+    sources = [
+      "test/run_test.h",
+      "video/video_loopback.cc",
+    ]
+
+    if (is_mac) {
+      sources += [ "test/mac/run_test.mm" ]
+    } else {
+      sources += [ "test/run_test.cc" ]
+    }
+    deps = [
+      ":video_quality_test",
+      "system_wrappers:metrics_default",
+      "test:field_trial",
+      "test:test_common",
+      "test:test_renderer",
+      "//testing/gmock",
+      "//testing/gtest",
+      "//third_party/gflags",
+    ]
+    if (is_clang && !is_nacl) {
+      # Suppress warnings from Chrome's Clang plugins.
+      # See http://code.google.com/p/webrtc/issues/detail?id=163 for details.
+      configs -= [ "//build/config/clang:find_bad_constructs" ]
+    }
+  }
 }
 
 source_set("webrtc_common") {