Adding support for simulcast and spatial layers into VideoQualityTest

The CL includes several changes:
- Adding flags describing the streams and spatial layers.
- Reorganizing the order of the flags, to make them easier to maintain.
- Adding a member .params_ to VideoQualityAnalyzer.
    (instead of passing it to every member function manually)
- Updating VideoAnalyzer to support simulcast.
    (select appropriate ssrc and fix timestamps which are sometimes increased by 1)
- VP9EncoderImpl already had code for automatic calculation of bitrate for each layer.
    Changing to first read bitrates and resolution ratios from the flags, if specified.
    If not specified, reverting to the old code are setting the values automatically.
- Changing the parameters in LayerFilteringTransport, replacing
    xx_discard_thresholds with selected_xx, to make it easier to use for the end user.

Review URL: https://codereview.webrtc.org/1353263005

Cr-Commit-Position: refs/heads/master@{#10215}

webrtc/video/full_stack.cc

@@ -23,6 +23,15 @@ class FullStackTest : public VideoQualityTest {
   }
 };
 
+// VideoQualityTest::Params params = {
+//   { ... },      // Common.
+//   { ... },      // Video-specific settings.
+//   { ... },      // Screenshare-specific settings.
+//   { ... },      // Analyzer settings.
+//   pipe,         // FakeNetworkPipe::Config
+//   { ... },      // Spatial scalability.
+//   logs          // bool
+// };
 
 TEST_F(FullStackTest, ParisQcifWithoutPacketLoss) {
   VideoQualityTest::Params paris_qcif = {
@@ -120,16 +129,16 @@ TEST_F(FullStackTest, ForemanCif1000kbps100msLimitedQueue) {
 
 TEST_F(FullStackTest, ScreenshareSlidesVP8_2TL) {
   VideoQualityTest::Params screenshare = {
-      {1850, 1110, 5, 50000, 200000, 2000000, "VP8", 2, 400000},
-      {},          // Video-specific.
-      {true, 10},  // Screenshare-specific.
+      {1850, 1110, 5, 50000, 200000, 2000000, "VP8", 2, 1, 400000},
+      {},
+      {true, 10},
       {"screenshare_slides", 0.0, 0.0, kFullStackTestDurationSecs}};
   RunTest(screenshare);
 }
 
 TEST_F(FullStackTest, ScreenshareSlidesVP8_2TL_Scroll) {
   VideoQualityTest::Params config = {
-      {1850, 1110 / 2, 5, 50000, 200000, 2000000, "VP8", 2, 400000},
+      {1850, 1110 / 2, 5, 50000, 200000, 2000000, "VP8", 2, 1, 400000},
       {},
       {true, 10, 2},
       {"screenshare_slides_scrolling", 0.0, 0.0, kFullStackTestDurationSecs}};
@@ -138,7 +147,7 @@ TEST_F(FullStackTest, ScreenshareSlidesVP8_2TL_Scroll) {
 
 TEST_F(FullStackTest, ScreenshareSlidesVP9_2TL) {
   VideoQualityTest::Params screenshare = {
-      {1850, 1110, 5, 50000, 200000, 2000000, "VP9", 2, 400000},
+      {1850, 1110, 5, 50000, 200000, 2000000, "VP9", 2, 1, 400000},
       {},
       {true, 10},
       {"screenshare_slides_vp9_2tl", 0.0, 0.0, kFullStackTestDurationSecs}};