Don't write spaces after semicolons in FMTP lines.

Reference: RFC 6184 section 8.2.1 and examples.

BUG=webrtc:5793
NOTRY=True

Review URL: https://codereview.webrtc.org/1888373002

Cr-Commit-Position: refs/heads/master@{#12383}
diff --git a/webrtc/api/webrtcsdp_unittest.cc b/webrtc/api/webrtcsdp_unittest.cc
index 2b63c79..f222b3f 100644
--- a/webrtc/api/webrtcsdp_unittest.cc
+++ b/webrtc/api/webrtcsdp_unittest.cc
@@ -2114,6 +2114,9 @@
   EXPECT_NE(std::string::npos, fmtp_value.find("level-asymmetry-allowed=1"));
   EXPECT_NE(std::string::npos, fmtp_value.find("packetization-mode=1"));
   EXPECT_NE(std::string::npos, fmtp_value.find("profile-level-id=42e01f"));
+  // Check that there are no spaces after semicolons.
+  // https://bugs.webrtc.org/5793
+  EXPECT_EQ(std::string::npos, fmtp_value.find("; "));
 }
 
 TEST_F(WebRtcSdpTest, DeserializeSessionDescription) {