Reland of Periodically update codec bit/frame rate settings.

Patch set 1 is a reland + trivial rebase.
Patch set >= 2 contains bug fixes.

> Original issue's description:
> > Fix bug in vie_encoder.cc which caused channel parameters not to be updated at regular intervals, as it was intended.
> >
> > That however exposes a bunch of failed test, so this CL also fixed a few other things:
> > * FakeEncoder should trust the configured FPS value rather than guesstimating itself based on the realtime clock, so as not to completely undershoot targets in offline mode. Also, compensate for key-frame overshoots when outputting delta frames.
> > * FrameDropper should not assuming incoming frame rate is 0 if no frames have been seen.
> > * Fix a bunch of test cases that started failing because they were relying on the fake encoder undershooting.
> > * Fix test
> >
> > BUG=7664
> >
> > Review-Url: https://codereview.webrtc.org/2883963002
> > Cr-Commit-Position: refs/heads/master@{#18473}
> > Committed: https://chromium.googlesource.com/external/webrtc/+/6431e21da672a5f3bbf166d3d4d98b171d015706

BUG=webrtc:7664

Review-Url: https://codereview.webrtc.org/2953053002
Cr-Commit-Position: refs/heads/master@{#18782}
diff --git a/webrtc/modules/video_coding/media_optimization.cc b/webrtc/modules/video_coding/media_optimization.cc
index ccd23f6..f0cbd62 100644
--- a/webrtc/modules/video_coding/media_optimization.cc
+++ b/webrtc/modules/video_coding/media_optimization.cc
@@ -118,7 +118,13 @@
   // Update encoding rates following protection settings.
   float target_video_bitrate_kbps =
       static_cast<float>(video_target_bitrate_) / 1000.0f;
-  frame_dropper_->SetRates(target_video_bitrate_kbps, incoming_frame_rate_);
+  float framerate = incoming_frame_rate_;
+  if (framerate == 0.0) {
+    // No framerate estimate available, use configured max framerate instead.
+    framerate = user_frame_rate_;
+  }
+
+  frame_dropper_->SetRates(target_video_bitrate_kbps, framerate);
 
   return video_target_bitrate_;
 }
diff --git a/webrtc/modules/video_coding/video_sender.cc b/webrtc/modules/video_coding/video_sender.cc
index ab77297..3dabbfc 100644
--- a/webrtc/modules/video_coding/video_sender.cc
+++ b/webrtc/modules/video_coding/video_sender.cc
@@ -103,6 +103,11 @@
     numLayers = sendCodec->VP8().numberOfTemporalLayers;
   } else if (sendCodec->codecType == kVideoCodecVP9) {
     numLayers = sendCodec->VP9().numberOfTemporalLayers;
+  } else if (sendCodec->codecType == kVideoCodecGeneric &&
+             sendCodec->numberOfSimulcastStreams > 0) {
+    // This is mainly for unit testing, disabling frame dropping.
+    // TODO(sprang): Add a better way to disable frame dropping.
+    numLayers = sendCodec->simulcastStream[0].numberOfTemporalLayers;
   } else {
     numLayers = 1;
   }
@@ -197,13 +202,17 @@
     input_frame_rate = current_codec_.maxFramerate;
 
   BitrateAllocation bitrate_allocation;
-  if (bitrate_allocator) {
-    bitrate_allocation = bitrate_allocator->GetAllocation(video_target_rate_bps,
-                                                          input_frame_rate);
-  } else {
-    DefaultVideoBitrateAllocator default_allocator(current_codec_);
-    bitrate_allocation = default_allocator.GetAllocation(video_target_rate_bps,
-                                                         input_frame_rate);
+  // Only call allocators if bitrate > 0 (ie, not suspended), otherwise they
+  // might cap the bitrate to the min bitrate configured.
+  if (target_bitrate_bps > 0) {
+    if (bitrate_allocator) {
+      bitrate_allocation = bitrate_allocator->GetAllocation(
+          video_target_rate_bps, input_frame_rate);
+    } else {
+      DefaultVideoBitrateAllocator default_allocator(current_codec_);
+      bitrate_allocation = default_allocator.GetAllocation(
+          video_target_rate_bps, input_frame_rate);
+    }
   }
   EncoderParameters new_encoder_params = {bitrate_allocation, params.loss_rate,
                                           params.rtt, input_frame_rate};
@@ -221,7 +230,7 @@
                                 encoder_params_.target_bitrate.get_sum_bps());
     target_rate = encoder_params_.target_bitrate;
   }
-  if (bitrate_updated_callback)
+  if (bitrate_updated_callback && target_rate.get_sum_bps() > 0)
     bitrate_updated_callback->OnBitrateAllocationUpdated(target_rate);
 }
 
@@ -236,7 +245,7 @@
   encoder_params.rtt = rtt;
   encoder_params = UpdateEncoderParameters(encoder_params, bitrate_allocator,
                                            target_bitrate_bps);
-  if (bitrate_updated_callback) {
+  if (bitrate_updated_callback && target_bitrate_bps > 0) {
     bitrate_updated_callback->OnBitrateAllocationUpdated(
         encoder_params.target_bitrate);
   }