[MediaStream] Add feature flag for enforcement of max frame rate

This CL adds a new feature flag that allows controlling how max frame
rates are enforced for MediaStreamTracks.
With the flag disabled (default), enforcement relies on system
configuration. With the flag enabled, enforcement relies on frame-rate
adjustments by the track.

Bug: 1152307
Change-Id: Idd158aa17a9c03215b59c68b89c8a0e74a7a2ece
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2557497Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830942}

third_party/blink/common/features.cc

@@ -824,5 +824,10 @@ const base::Feature kLoadingTasksUnfreezable{"LoadingTasksUnfreezable",
 // noopener behavior by default. TODO(crbug.com/898942): Remove in Chrome 95.
 const base::Feature kTargetBlankImpliesNoOpener{
     "TargetBlankImpliesNoOpener", base::FEATURE_ENABLED_BY_DEFAULT};
+
+// Controls how max frame rates are enforced in MediaStreamTracks.
+// TODO(crbug.com/1152307): Remove in M91.
+const base::Feature kMediaStreamTrackUseConfigMaxFrameRate{
+    "MediaStreamTrackUseConfigMaxFrameRate", base::FEATURE_DISABLED_BY_DEFAULT};
 }  // namespace features
 }  // namespace blink

third_party/blink/public/common/features.h

@@ -338,6 +338,9 @@ BLINK_COMMON_EXPORT extern const base::Feature kWebRtcLibvpxEncodeNV12;
 BLINK_COMMON_EXPORT extern const base::Feature kLoadingTasksUnfreezable;
 
 BLINK_COMMON_EXPORT extern const base::Feature kTargetBlankImpliesNoOpener;
+
+BLINK_COMMON_EXPORT extern const base::Feature
+    kMediaStreamTrackUseConfigMaxFrameRate;
 }  // namespace features
 }  // namespace blink
 

third_party/blink/renderer/modules/mediastream/video_track_adapter.cc

@@ -22,6 +22,7 @@
 #include "media/base/bind_to_current_loop.h"
 #include "media/base/limits.h"
 #include "media/base/video_util.h"
+#include "third_party/blink/public/common/features.h"
 #include "third_party/blink/public/platform/platform.h"
 #include "third_party/blink/renderer/modules/mediastream/video_track_adapter_settings.h"
 #include "third_party/blink/renderer/platform/scheduler/public/post_cross_thread_task.h"
@@ -409,7 +410,11 @@ bool VideoTrackAdapter::VideoFrameResolutionAdapter::MaybeDropFrame(
   DCHECK_CALLED_ON_VALID_THREAD(io_thread_checker_);
 
   // Do not drop frames if max frame rate hasn't been specified.
-  if (settings_.max_frame_rate() == 0.0f) {
+  if (settings_.max_frame_rate() == 0.0f ||
+      (base::FeatureList::IsEnabled(
+           features::kMediaStreamTrackUseConfigMaxFrameRate) &&
+       source_frame_rate > 0 &&
+       source_frame_rate <= settings_.max_frame_rate())) {
     last_time_stamp_ = frame.timestamp();
     return false;
   }