Adding third_party/openh264 build files for encoding

content/test/BUILD.gn

Index: content/test/BUILD.gn
diff --git a/content/test/BUILD.gn b/content/test/BUILD.gn
index 503aee2d7ba6ff76ef7093ae42f40ca60ba10129..8ba24a989132eeefc4c0d79c1a548f96844bf53c 100644
--- a/content/test/BUILD.gn
+++ b/content/test/BUILD.gn
@@ -768,6 +768,11 @@ test("content_unittests") {
   if (is_mac && use_openssl) {
     deps += [ "//third_party/boringssl" ]
   }
+
+  if (use_openh264) {
+    sources += [ "../browser/media/openh264_unittests.cc" ]
+    deps += [ "//third_party/openh264/testing:openh264_testing" ]
+  }
 }
 
 test("content_perftests") {