Move VideoCodecTest configuration classes to api/test.

These files are required when implementing tests based on the test fixture,
and should be exposed as part of the test api.

This CL also removes a usage of stringstream and fixes some chromium-style
lint issues.

Bug: webrtc:8982, webrtc:163
Change-Id: I132aea0da79a79587887f21897236fc9802b7574
Reviewed-on: https://webrtc-review.googlesource.com/74586
Commit-Queue: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23346}
diff --git a/api/test/create_videocodec_test_fixture.h b/api/test/create_videocodec_test_fixture.h
index 24e17fd..7a44f6b 100644
--- a/api/test/create_videocodec_test_fixture.h
+++ b/api/test/create_videocodec_test_fixture.h
@@ -16,17 +16,15 @@
 #include "api/test/videocodec_test_fixture.h"
 #include "api/video_codecs/video_decoder_factory.h"
 #include "api/video_codecs/video_encoder_factory.h"
-#include "modules/video_coding/codecs/test/test_config.h"
 
 namespace webrtc {
 namespace test {
 
-std::unique_ptr<VideoCodecTestFixture>
-CreateVideoCodecTestFixture(const TestConfig& config);
+std::unique_ptr<VideoCodecTestFixture> CreateVideoCodecTestFixture(
+    const VideoCodecTestFixture::Config& config);
 
-std::unique_ptr<VideoCodecTestFixture>
-CreateVideoCodecTestFixture(
-    const TestConfig& config,
+std::unique_ptr<VideoCodecTestFixture> CreateVideoCodecTestFixture(
+    const VideoCodecTestFixture::Config& config,
     std::unique_ptr<VideoDecoderFactory> decoder_factory,
     std::unique_ptr<VideoEncoderFactory> encoder_factory);