Reject negative values for "b=AS".

webrtc/pc/webrtcsdp.cc

Index: webrtc/pc/webrtcsdp.cc
diff --git a/webrtc/pc/webrtcsdp.cc b/webrtc/pc/webrtcsdp.cc
index d9ed4255aa032baa0688761e7871ee867ba8b68f..bc2ec89645d37e1667444d38b29c837be0d8fd3a 100644
--- a/webrtc/pc/webrtcsdp.cc
+++ b/webrtc/pc/webrtcsdp.cc
@@ -2719,6 +2719,9 @@ bool ParseContent(const std::string& message,
           if (!GetValueFromString(line, bandwidth, &b, error)) {
             return false;
           }
+          if (b < 0) {
+            return ParseFailed(line, "b=AS value can't be negative.", error);
+          }
           // We should never use more than the default bandwidth for RTP-based
           // data channels. Don't allow SDP to set the bandwidth, because
           // that would give JS the opportunity to "break the Internet".