Adding third_party/openh264/src, build files and unittests

content/content_tests.gypi

Index: content/content_tests.gypi
diff --git a/content/content_tests.gypi b/content/content_tests.gypi
index 75789a556387af02c320840e79c51cc0932a19c0..7914515c1e1b744fd8b4a09e991dac1b6192eeab 100644
--- a/content/content_tests.gypi
+++ b/content/content_tests.gypi
@@ -1291,6 +1291,14 @@
                 '../third_party/boringssl/boringssl.gyp:boringssl',
               ],
             }],
+            ['build_openh264==1', {
+              'sources': [
+                'browser/media/openh264_unittests.cc',
+              ],
+              'dependencies': [
+                '../third_party/openh264/testing/openh264_testing.gyp:openh264_testing',
+              ],
+            }],
           ],
         },
         {