Fix target bitrate handling for a single layer VP9 screenshare

For a single layer vp9, the target bitrate was not set correctly. This
may cause a problem for screenshare case, since target bitrate is
respected in that case. If it were less than a min bitrate, the only
spatial layer was permanently disabled.

Bug: webrtc:10257
Change-Id: I0980349adfc2970f810acc51a3e2a31ecbb2bbd2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/125681
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26970}
diff --git a/modules/video_coding/video_codec_initializer_unittest.cc b/modules/video_coding/video_codec_initializer_unittest.cc
index 6734b7e..0f2d9f1 100644
--- a/modules/video_coding/video_codec_initializer_unittest.cc
+++ b/modules/video_coding/video_codec_initializer_unittest.cc
@@ -297,6 +297,18 @@
 }
 
 TEST_F(VideoCodecInitializerTest,
+       Vp9SingleSpatialLayerTargetBitrateIsEqualToCodecMaxBitrate) {
+  SetUpFor(VideoCodecType::kVideoCodecVP9, 1, 1, true);
+  VideoStream stream = DefaultStream();
+  stream.num_temporal_layers = 1;
+  streams_.push_back(stream);
+
+  EXPECT_TRUE(InitializeCodec());
+  EXPECT_EQ(codec_out_.spatialLayers[0].targetBitrate,
+            kDefaultMaxBitrateBps / 1000);
+}
+
+TEST_F(VideoCodecInitializerTest,
        Vp9KeepBitrateLimitsIfNumberOfSpatialLayersIsReducedToOne) {
   // Request 3 spatial layers for 320x180 input. Actual number of layers will be
   // reduced to 1 due to low input resolution but SVC bitrate limits should be