Refactor rtc_unittests into several targets.

webrtc/sdk/objc/Framework/UnitTests/avformatmappertests.mm

Index: webrtc/sdk/objc/Framework/UnitTests/avformatmappertests.mm
diff --git a/webrtc/sdk/objc/Framework/UnitTests/avformatmappertests.mm b/webrtc/sdk/objc/Framework/UnitTests/avformatmappertests.mm
index 623ac6f7301f228d2c14447a1f0bd8c1d414fdf0..5f8cacbc46f2cb0adc34992bf85350d019d3ab00 100644
--- a/webrtc/sdk/objc/Framework/UnitTests/avformatmappertests.mm
+++ b/webrtc/sdk/objc/Framework/UnitTests/avformatmappertests.mm
@@ -160,7 +160,7 @@ TEST(AVFormatMapperTest, SuportedCricketFormats) {
       webrtc::GetSupportedVideoFormatsForDevice(mockDevice);
 
   // then
-  EXPECT_EQ(1, result.size());
+  EXPECT_EQ(1u, result.size());
 
   // make sure the set has the expected format
   EXPECT_EQ(expectedFormat, *result.begin());