Fix test bug introduced in r11101.

BUG=chromium:572995
R=pbos@webrtc.org

Review URL: https://codereview.webrtc.org/1578223002 .

Cr-Commit-Position: refs/heads/master@{#11224}

webrtc/call/rampup_tests.cc

@@ -87,6 +87,10 @@ test::PacketTransport* RampUpTester::CreateSendTransport(Call* sender_call) {
   return send_transport_;
 }
 
+size_t RampUpTester::GetNumVideoStreams() const {
+  return num_video_streams_;
+}
+
 void RampUpTester::ModifyVideoConfigs(
     VideoSendStream::Config* send_config,
     std::vector<VideoReceiveStream::Config>* receive_configs,

webrtc/call/rampup_tests.h

@@ -39,6 +39,8 @@ class RampUpTester : public test::EndToEndTest {
                bool red);
   ~RampUpTester() override;
 
+  size_t GetNumVideoStreams() const override;
+
   void PerformTest() override;
 
  protected: