Move VP8 SupportsScalabilityMode utility to its own build target

Intended to let Vp8TemporalLayersFactory (an api/ target) reuse
this function, without depending on the codec implementation, and
without introducing a dependency cycle with the webrtc_vp8 build
target.

Bug: webrtc:11607
Change-Id: I671422e994e1005da8c7d768e8dd8ff795553e51
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/261308
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36816}

modules/video_coding/codecs/vp8/include/vp8.h

@@ -15,7 +15,6 @@
 #include <vector>
 
 #include "absl/base/attributes.h"
-#include "api/video_codecs/scalability_mode.h"
 #include "api/video_codecs/video_encoder.h"
 #include "api/video_codecs/vp8_frame_buffer_controller.h"
 #include "modules/video_coding/include/video_codec_interface.h"
@@ -40,7 +39,6 @@ class VP8Encoder {
 
   static std::unique_ptr<VideoEncoder> Create();
   static std::unique_ptr<VideoEncoder> Create(Settings settings);
-  static bool SupportsScalabilityMode(ScalabilityMode scalability_mode);
 
   ABSL_DEPRECATED("")
   static std::unique_ptr<VideoEncoder> Create(

modules/video_coding/codecs/vp8/libvpx_vp8_encoder.cc

@@ -49,9 +49,6 @@ constexpr char kVP8IosMaxNumberOfThreadFieldTrial[] =
 constexpr char kVP8IosMaxNumberOfThreadFieldTrialParameter[] = "max_thread";
 #endif
 
-constexpr ScalabilityMode kSupportedScalabilityModes[] = {
-    ScalabilityMode::kL1T1, ScalabilityMode::kL1T2, ScalabilityMode::kL1T3};
-
 constexpr char kVp8ForcePartitionResilience[] =
     "WebRTC-VP8-ForcePartitionResilience";
 
@@ -233,15 +230,6 @@ std::unique_ptr<VideoEncoder> VP8Encoder::Create(
                                             std::move(settings));
 }
 
-bool VP8Encoder::SupportsScalabilityMode(ScalabilityMode scalability_mode) {
-  for (const auto& entry : kSupportedScalabilityModes) {
-    if (entry == scalability_mode) {
-      return true;
-    }
-  }
-  return false;
-}
-
 vpx_enc_frame_flags_t LibvpxVp8Encoder::EncodeFlags(
     const Vp8FrameConfig& references) {
   RTC_DCHECK(!references.drop_frame);

modules/video_coding/codecs/vp8/vp8_scalability.cc

@@ -0,0 +1,26 @@
+/*
+ *  Copyright (c) 2022 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "modules/video_coding/codecs/vp8/vp8_scalability.h"
+
+namespace webrtc {
+
+bool VP8SupportsScalabilityMode(ScalabilityMode scalability_mode) {
+  constexpr ScalabilityMode kSupportedScalabilityModes[] = {
+      ScalabilityMode::kL1T1, ScalabilityMode::kL1T2, ScalabilityMode::kL1T3};
+  for (const auto& entry : kSupportedScalabilityModes) {
+    if (entry == scalability_mode) {
+      return true;
+    }
+  }
+  return false;
+}
+
+}  // namespace webrtc

modules/video_coding/codecs/vp8/vp8_scalability.h

@@ -0,0 +1,22 @@
+/*
+ *  Copyright (c) 2022 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef MODULES_VIDEO_CODING_CODECS_VP8_VP8_SCALABILITY_H_
+#define MODULES_VIDEO_CODING_CODECS_VP8_VP8_SCALABILITY_H_
+
+#include "api/video_codecs/scalability_mode.h"
+
+namespace webrtc {
+
+bool VP8SupportsScalabilityMode(ScalabilityMode scalability_mode);
+
+}  // namespace webrtc
+
+#endif  // MODULES_VIDEO_CODING_CODECS_VP8_VP8_SCALABILITY_H_