--- a/media/webrtc/signaling/gtest/jsep_session_unittest.cpp
+++ b/media/webrtc/signaling/gtest/jsep_session_unittest.cpp
@@ -1002,20 +1002,20 @@ protected:
   void
   ValidateDisabledMSection(const SdpMediaSection* msection)
   {
     ASSERT_EQ(1U, msection->GetFormats().size());
 
     auto& attrs = msection->GetAttributeList();
     ASSERT_TRUE(attrs.HasAttribute(SdpAttribute::kMidAttribute));
     ASSERT_TRUE(attrs.HasAttribute(SdpAttribute::kDirectionAttribute));
+    ASSERT_FALSE(attrs.HasAttribute(SdpAttribute::kBundleOnlyAttribute));
     ASSERT_EQ(SdpDirectionAttribute::kInactive,
               msection->GetDirectionAttribute().mValue);
-    // attribute list is missing a length function to check if these are
-    // all the attributes in it
+    ASSERT_EQ(3U, attrs.Count());
     if (msection->GetMediaType() == SdpMediaSection::kAudio) {
       ASSERT_EQ("0", msection->GetFormats()[0]);
       const SdpRtpmapAttributeList::Rtpmap* rtpmap(msection->FindRtpmap("0"));
       ASSERT_TRUE(rtpmap);
       ASSERT_EQ("0", rtpmap->pt);
       ASSERT_EQ("PCMU", rtpmap->name);
     } else if (msection->GetMediaType() == SdpMediaSection::kVideo) {
       ASSERT_EQ("120", msection->GetFormats()[0]);

--- a/media/webrtc/signaling/src/sdp/SdpAttributeList.h
+++ b/media/webrtc/signaling/src/sdp/SdpAttributeList.h
@@ -36,16 +36,17 @@ public:
 
   virtual bool HasAttribute(AttributeType type, bool sessionFallback) const = 0;
   virtual const SdpAttribute* GetAttribute(AttributeType type,
                                            bool sessionFallback) const = 0;
   // The setter takes an attribute of any type, and takes ownership
   virtual void SetAttribute(SdpAttribute* attr) = 0;
   virtual void RemoveAttribute(AttributeType type) = 0;
   virtual void Clear() = 0;
+  virtual uint32_t Count() const = 0;
 
   virtual const SdpConnectionAttribute& GetConnection() const = 0;
   virtual const SdpOptionsAttribute& GetIceOptions() const = 0;
   virtual const SdpRtcpAttribute& GetRtcp() const = 0;
   virtual const SdpRemoteCandidatesAttribute& GetRemoteCandidates() const = 0;
   virtual const SdpSetupAttribute& GetSetup() const = 0;
   virtual const SdpDtlsMessageAttribute& GetDtlsMessage() const = 0;
 

--- a/media/webrtc/signaling/src/sdp/SipccSdpAttributeList.cpp
+++ b/media/webrtc/signaling/src/sdp/SipccSdpAttributeList.cpp
@@ -65,16 +65,28 @@ SipccSdpAttributeList::RemoveAttribute(A
 void
 SipccSdpAttributeList::Clear()
 {
   for (size_t i = 0; i < kNumAttributeTypes; ++i) {
     RemoveAttribute(static_cast<AttributeType>(i));
   }
 }
 
+uint32_t
+SipccSdpAttributeList::Count() const
+{
+  uint32_t count = 0;
+  for (size_t i = 0; i < kNumAttributeTypes; ++i) {
+    if (mAttributes[i]) {
+      count++;
+    }
+  }
+  return count;
+}
+
 void
 SipccSdpAttributeList::SetAttribute(SdpAttribute* attr)
 {
   if (!IsAllowedHere(attr->GetType())) {
     MOZ_ASSERT(false, "This type of attribute is not allowed here");
     return;
   }
   RemoveAttribute(attr->GetType());

--- a/media/webrtc/signaling/src/sdp/SipccSdpAttributeList.h
+++ b/media/webrtc/signaling/src/sdp/SipccSdpAttributeList.h
@@ -32,16 +32,17 @@ public:
 
   virtual bool HasAttribute(AttributeType type,
                             bool sessionFallback) const override;
   virtual const SdpAttribute* GetAttribute(
       AttributeType type, bool sessionFallback) const override;
   virtual void SetAttribute(SdpAttribute* attr) override;
   virtual void RemoveAttribute(AttributeType type) override;
   virtual void Clear() override;
+  virtual uint32_t Count() const override;
 
   virtual const SdpConnectionAttribute& GetConnection() const override;
   virtual const SdpFingerprintAttributeList& GetFingerprint() const
       override;
   virtual const SdpGroupAttributeList& GetGroup() const override;
   virtual const SdpOptionsAttribute& GetIceOptions() const override;
   virtual const SdpRtcpAttribute& GetRtcp() const override;
   virtual const SdpRemoteCandidatesAttribute& GetRemoteCandidates() const