Reland of quest keyframes more frequently on stream start/decoding error. (patchset #1 id:1 of https://codereview.chromium.org/2995153002/ )

Reason for revert:
iOS workaround.

Original issue's description:
> Revert of quest keyframes more frequently on stream start/decoding error. (patchset #2 id:170001 of https://codereview.webrtc.org/2996823002/ )
>
> Reason for revert:
> Causes iOS H264 calls received in the background to have increased delay before being able to decode stream from sender due to not having a keyframe.
>
> Original issue's description:
> > Reland of quest keyframes more frequently on stream start/decoding error. (patchset #1 id:1 of https://codereview.chromium.org/2994043002/ )
> >
> > Reason for revert:
> > Create fix CL.
> >
> > Original issue's description:
> > > Revert of Request keyframes more frequently on stream start/decoding error. (patchset #1 id:1 of https://codereview.webrtc.org/2993793002/ )
> > >
> > > Reason for revert:
> > > Broke downstream test that was waiting for 5 keyframes to be received within 10 seconds. Maybe the issue is that "stats_callback_->OnCompleteFrame(frame->num_references == 0, ..." was changed to "frame->is_keyframe()"?
> > >
> > > Original issue's description:
> > > > Request keyframes more frequently on stream start/decoding error.
> > > >
> > > > In this CL:
> > > >  - Added FrameObject::is_keyframe() convinience function.
> > > >  - Moved logic to request keyframes on decoding error from VideoReceived to
> > > >    VideoReceiveStream.
> > > >  - Added keyframe_required as a parameter to FrameBuffer::NextFrame.
> > > >
> > > > BUG=webrtc:8074
> > > >
> > > > Review-Url: https://codereview.webrtc.org/2993793002
> > > > Cr-Commit-Position: refs/heads/master@{#19280}
> > > > Committed: https://chromium.googlesource.com/external/webrtc/+/26b48043581735eed6e36b95fae6f5b1bcf8cfb5
> > >
> > > TBR=terelius@webrtc.org,stefan@webrtc.org,noahric@chromium.org,philipel@webrtc.org
> > > # Skipping CQ checks because original CL landed less than 1 days ago.
> > > NOPRESUBMIT=true
> > > NOTREECHECKS=true
> > > NOTRY=true
> > > BUG=webrtc:8074
> > >
> > > Review-Url: https://codereview.webrtc.org/2994043002
> > > Cr-Commit-Position: refs/heads/master@{#19295}
> > > Committed: https://chromium.googlesource.com/external/webrtc/+/77a983185f57628cd5955bd2c0a1bf71c30439bb
> >
> > TBR=terelius@webrtc.org,stefan@webrtc.org,noahric@chromium.org,deadbeef@webrtc.org
> > # Skipping CQ checks because original CL landed less than 1 days ago.
> > BUG=webrtc:8074
> >
> > Review-Url: https://codereview.webrtc.org/2996823002
> > Cr-Commit-Position: refs/heads/master@{#19324}
> > Committed: https://chromium.googlesource.com/external/webrtc/+/628ac5964e32e66083a6ab14dceac6cb2cabe345
>
> TBR=terelius@webrtc.org,stefan@webrtc.org,noahric@chromium.org,deadbeef@webrtc.org,philipel@webrtc.org
> # Not skipping CQ checks because original CL landed more than 1 days ago.
> BUG=webrtc:8074
>
> Review-Url: https://codereview.webrtc.org/2995153002
> Cr-Commit-Position: refs/heads/master@{#19392}
> Committed: https://chromium.googlesource.com/external/webrtc/+/53959fcc2ba580e7c87231708e5b4af7906f6836

TBR=terelius@webrtc.org,stefan@webrtc.org,noahric@chromium.org,deadbeef@webrtc.org,tkchin@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.

BUG=webrtc:8074

Review-Url: https://codereview.webrtc.org/2996153003
Cr-Original-Commit-Position: refs/heads/master@{#19410}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 3042c2d5e0e400d96437e041151995fd96f46ff4

modules/video_coding/frame_buffer2.cc

diff --git a/modules/video_coding/frame_buffer2.cc b/modules/video_coding/frame_buffer2.cc
index 2540ae5..016a24e 100644
--- a/modules/video_coding/frame_buffer2.cc
+++ b/modules/video_coding/frame_buffer2.cc
@@ -59,7 +59,8 @@
 
 FrameBuffer::ReturnReason FrameBuffer::NextFrame(
     int64_t max_wait_time_ms,
-    std::unique_ptr<FrameObject>* frame_out) {
+    std::unique_ptr<FrameObject>* frame_out,
+    bool keyframe_required) {
   TRACE_EVENT0("webrtc", "FrameBuffer::NextFrame");
   int64_t latest_return_time_ms =
       clock_->TimeInMilliseconds() + max_wait_time_ms;
@@ -105,6 +106,10 @@
         }
 
         FrameObject* frame = frame_it->second.frame.get();
+
+        if (keyframe_required && !frame->is_keyframe())
+          continue;
+
         next_frame_it_ = frame_it;
         if (frame->RenderTime() == -1)
           frame->SetRenderTime(timing_->RenderTimeMs(frame->timestamp, now_ms));
@@ -279,7 +284,7 @@
   TRACE_EVENT0("webrtc", "FrameBuffer::InsertFrame");
   RTC_DCHECK(frame);
   if (stats_callback_)
-    stats_callback_->OnCompleteFrame(frame->num_references == 0, frame->size());
+    stats_callback_->OnCompleteFrame(frame->is_keyframe(), frame->size());
   FrameKey key(frame->picture_id, frame->spatial_layer);
 
   rtc::CritScope lock(&crit_);
@@ -307,7 +312,7 @@
   if (last_decoded_frame_it_ != frames_.end() &&
       key <= last_decoded_frame_it_->first) {
     if (AheadOf(frame->timestamp, last_decoded_frame_timestamp_) &&
-        frame->num_references == 0) {
+        frame->is_keyframe()) {
       // If this frame has a newer timestamp but an earlier picture id then we
       // assume there has been a jump in the picture id due to some encoder
       // reconfiguration or some other reason. Even though this is not according