message: Fix tests in WebRtcVideoChannelBaseTest.
  If rtc_libvpx_build_vp9=false, some tests fail because
  BuiltinVideoEncoderFactory / DecoderFactory doesn't support VP9.
  Cr-Commit-Position: refs/heads/master@{#32028}
diff: @@ -2262,6 +2262,8 @@ TEST_F(WebRtcVideoChannelBaseTest, TwoStreamsSendAndReceive) {
  TwoStreamsSendAndReceive(codec);
  }
  +#if defined(RTC_ENABLE_VP9)
  +
  TEST_F(WebRtcVideoChannelBaseTest, RequestEncoderFallback) {
  cricket::VideoSendParameters parameters;
  parameters.codecs.push_back(GetEngineCodec("VP9"));
  @@ -2398,6 +2400,8 @@ TEST_F(WebRtcVideoChannelBaseTest,
  EXPECT_THAT(codec.params, Contains(Pair(kParam, kPing)));
  }
  +#endif // defined(RTC_ENABLE_VP9)
  +
  class WebRtcVideoChannelTest : public WebRtcVideoEngineTest {
  public:
  WebRtcVideoChannelTest() : WebRtcVideoChannelTest("") {}
  