Add unit tests for avfoundation format mapper functions and fix wrong implementation.

webrtc/BUILD.gn

Index: webrtc/BUILD.gn
diff --git a/webrtc/BUILD.gn b/webrtc/BUILD.gn
index 242d8ea981008598045748609b6648a2cbc9f760..8de83c90a1d02f4b8e22fe42e89f43ab6f4cf0ba 100644
--- a/webrtc/BUILD.gn
+++ b/webrtc/BUILD.gn
@@ -530,6 +530,7 @@ if (rtc_include_tests) {
       deps += [
         "sdk:rtc_sdk_peerconnection_objc",
         "system_wrappers:system_wrappers_default",
+        "//third_party/ocmock",
       ]
       sources += [
         "sdk/objc/Framework/UnitTests/RTCConfigurationTest.mm",
@@ -538,6 +539,7 @@ if (rtc_include_tests) {
         "sdk/objc/Framework/UnitTests/RTCIceServerTest.mm",
         "sdk/objc/Framework/UnitTests/RTCMediaConstraintsTest.mm",
         "sdk/objc/Framework/UnitTests/RTCSessionDescriptionTest.mm",
+        "sdk/objc/Framework/UnitTests/avformatmappertests.mm",
       ]
 
       # TODO(tkchin): Cleanup this warning.