[MediaStream] Enforce max frame rates

Prior to this CL, explicit max frame rates were not enforced
if the configured frame rate for the source was less than or
equal to the requested max frame rate. This has led to problems
with webcams that produce a higher frame rate than configured.

This CL changes the VideoTrackAdapter so that frame rate
adjustments are disabled only for tracks that do not explicitly
request a maximum frame rate.

Bug: 1133796
Change-Id: I2e3769493449b552f9440c2a809b512bf9e3690c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2534952
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Marina Ciocea <marinaciocea@chromium.org>
Auto-Submit: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Marina Ciocea <marinaciocea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826877}

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

@@ -408,11 +408,8 @@ bool VideoTrackAdapter::VideoFrameResolutionAdapter::MaybeDropFrame(
     media::VideoCaptureFrameDropReason* reason) {
   DCHECK_CALLED_ON_VALID_THREAD(io_thread_checker_);
 
-  // Do not drop frames if max frame rate hasn't been specified or the source
-  // frame rate is known and is lower than max.
-  if (settings_.max_frame_rate() == 0.0f ||
-      (source_frame_rate > 0 &&
-       source_frame_rate <= settings_.max_frame_rate())) {
+  // Do not drop frames if max frame rate hasn't been specified.
+  if (settings_.max_frame_rate() == 0.0f) {
     last_time_stamp_ = frame.timestamp();
     return false;
   }