Fix suspend below min bitrate in new API by making it possible to set min bitrate at the receive-side.

In addition to this the ramp-up tests are refactored to use a receive call instead of only a remote bitrate estimator, and to make use of BaseTest.

BUG=webrtc:4836

Review URL: https://codereview.webrtc.org/1368943002

Cr-Commit-Position: refs/heads/master@{#10087}
diff --git a/webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.h b/webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.h
index 6d7390e..e867ff7 100644
--- a/webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.h
+++ b/webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.h
@@ -45,7 +45,8 @@
   bool LatestEstimate(std::vector<unsigned int>* ssrcs,
                       unsigned int* bitrate_bps) const override;
   bool GetStats(ReceiveBandwidthEstimatorStats* output) const override;
-  void OnRttUpdate(int64_t avg_rtt_ms, int64_t max_rtt_ms) override;
+  void OnRttUpdate(int64_t avg_rtt_ms, int64_t max_rtt_ms) override {}
+  void SetMinBitrate(int min_bitrate_bps) override {}
   int64_t TimeUntilNextProcess() override;
   int32_t Process() override;