Adding third_party/openh264/src, build files and unittests

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index d1791b096917fd38cc9a71d4fbd0aa028737d26f..952821489a0cb9491e204d58d2f52ac1eea996e3 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -72,7 +72,6 @@ group("both_gn_and_gyp") {
     "//skia:skia_unittests",
     "//sql:sql_unittests",
     "//sync:sync_unit_tests",
-    "//third_party/openh264/tests:openh264_unittests",
     "//ui/base:ui_base_unittests",
     "//ui/gfx:gfx_unittests",
     "//url:url_unittests",
@@ -664,6 +663,15 @@ group("gn_only") {
   if (use_libfuzzer) {
     deps += [ "//testing/libfuzzer:libfuzzer_main" ]
   }
+
+  if (use_openh264) {
+    deps += [
+      "//third_party/openh264:openh264_common",
+      "//third_party/openh264:openh264_processing",
+      "//third_party/openh264:openh264_encoder",
+      "//third_party/openh264:openh264_decoder",
+    ]
+  }
 }
 
 group("gn_mojo_targets") {