diff --git a/testing/web-platform/tests/webrtc/legacy/munge-dont.html b/testing/web-platform/tests/webrtc/legacy/munge-dont.html
new file mode 100644
index 0000000000000..037b7aaa264dd
--- /dev/null
+++ b/testing/web-platform/tests/webrtc/legacy/munge-dont.html
@@ -0,0 +1,871 @@
+<
+!
+doctype
+html
+>
+<
+meta
+charset
+=
+utf
+-
+8
+>
+<
+meta
+name
+=
+"
+timeout
+"
+content
+=
+"
+long
+"
+>
+<
+title
+>
+SDP
+munging
+is
+a
+bad
+idea
+<
+/
+title
+>
+<
+script
+src
+=
+"
+/
+resources
+/
+testharness
+.
+js
+"
+>
+<
+/
+script
+>
+<
+script
+src
+=
+"
+/
+resources
+/
+testharnessreport
+.
+js
+"
+>
+<
+/
+script
+>
+<
+script
+>
+'
+use
+strict
+'
+;
+const
+sdp
+=
+v
+=
+0
+o
+=
+-
+0
+3
+IN
+IP4
+127
+.
+0
+.
+0
+.
+1
+s
+=
+-
+t
+=
+0
+0
+m
+=
+video
+9
+UDP
+/
+TLS
+/
+RTP
+/
+SAVPF
+100
+c
+=
+IN
+IP4
+0
+.
+0
+.
+0
+.
+0
+a
+=
+rtcp
+-
+mux
+a
+=
+sendonly
+a
+=
+mid
+:
+video
+a
+=
+rtpmap
+:
+100
+VP8
+/
+90000
+a
+=
+fmtp
+:
+100
+max
+-
+fr
+=
+30
+;
+max
+-
+fs
+=
+3600
+a
+=
+fingerprint
+:
+sha
+-
+256
+A7
+:
+24
+:
+72
+:
+CA
+:
+6E
+:
+02
+:
+55
+:
+39
+:
+BA
+:
+66
+:
+DF
+:
+6E
+:
+CC
+:
+4C
+:
+D8
+:
+B0
+:
+1A
+:
+BF
+:
+1A
+:
+56
+:
+65
+:
+7D
+:
+F4
+:
+03
+:
+AD
+:
+7E
+:
+77
+:
+43
+:
+2A
+:
+29
+:
+EC
+:
+93
+a
+=
+ice
+-
+ufrag
+:
+ETEn
+a
+=
+ice
+-
+pwd
+:
+OtSK0WpNtpUjkY4
++
+86js7Z
+/
+l
+;
+const
+candidateString
+=
+'
+candidate
+:
+1905690388
+1
+udp
+2113937151
+192
+.
+168
+.
+0
+.
+1
+58041
+typ
+host
+generation
+0
+ufrag
+thC8
+'
+;
+/
+/
+See
+https
+:
+/
+/
+bugs
+.
+chromium
+.
+org
+/
+p
+/
+chromium
+/
+issues
+/
+detail
+?
+id
+=
+662898
+/
+/
+and
+https
+:
+/
+/
+bugs
+.
+chromium
+.
+org
+/
+p
+/
+chromium
+/
+issues
+/
+detail
+?
+id
+=
+823036
+/
+/
+for
+why
+neither
+of
+these
+is
+feasible
+to
+enforce
+.
+/
+/
+Note
+that
+this
+does
+not
+restrict
+creating
+a
+/
+/
+new
+RTCSessionDescription
+with
+a
+modified
+copy
+.
+test
+(
+(
+)
+=
+>
+{
+const
+desc
+=
+new
+RTCSessionDescription
+(
+{
+type
+:
+'
+offer
+'
+sdp
+}
+)
+;
+assert_throws_js
+(
+TypeError
+(
+)
+=
+>
+{
+desc
+.
+type
+=
+'
+answer
+'
+;
+}
+)
+;
+}
+'
+RTCSessionDescription
+.
+type
+is
+read
+-
+only
+'
+)
+;
+test
+(
+(
+)
+=
+>
+{
+const
+desc
+=
+new
+RTCSessionDescription
+(
+{
+type
+:
+'
+offer
+'
+sdp
+}
+)
+;
+assert_throws_js
+(
+TypeError
+(
+)
+=
+>
+{
+desc
+.
+sdp
++
+=
+'
+a
+=
+dont
+-
+modify
+-
+me
+\
+r
+\
+n
+'
+;
+}
+)
+;
+}
+'
+RTCSessionDescription
+.
+sdp
+is
+read
+-
+only
+'
+)
+;
+test
+(
+(
+)
+=
+>
+{
+const
+candidate
+=
+new
+RTCIceCandidate
+(
+{
+sdpMid
+:
+'
+0
+'
+candidate
+:
+candidateString
+}
+)
+;
+assert_throws_js
+(
+TypeError
+(
+)
+=
+>
+{
+candidate
+.
+candidate
++
+=
+'
+myattribute
+value
+'
+;
+}
+)
+;
+}
+'
+RTCIceCandidate
+.
+candidate
+is
+read
+-
+only
+'
+)
+;
+/
+/
+https
+:
+/
+/
+w3c
+.
+github
+.
+io
+/
+webrtc
+-
+pc
+/
+#
+dom
+-
+peerconnection
+-
+setlocaldescription
+/
+/
+If
+type
+is
+"
+offer
+"
+and
+sdp
+is
+not
+the
+empty
+string
+and
+not
+equal
+to
+/
+/
+connection
+.
+[
+[
+LastCreatedOffer
+]
+]
+then
+return
+a
+promise
+rejected
+with
+a
+/
+/
+newly
+created
+InvalidModificationError
+and
+abort
+these
+steps
+.
+promise_test
+(
+async
+t
+=
+>
+{
+const
+pc
+=
+new
+RTCPeerConnection
+(
+)
+;
+t
+.
+add_cleanup
+(
+(
+)
+=
+>
+pc
+.
+close
+(
+)
+)
+;
+pc
+.
+addTransceiver
+(
+'
+audio
+'
+)
+;
+const
+offer
+=
+await
+pc
+.
+createOffer
+(
+)
+;
+return
+promise_rejects_dom
+(
+t
+'
+InvalidModificationError
+'
+pc
+.
+setLocalDescription
+(
+{
+type
+:
+'
+offer
+'
+sdp
+:
+offer
+.
+sdp
++
+'
+a
+=
+munging
+-
+is
+-
+not
+-
+good
+\
+r
+\
+n
+'
+}
+)
+)
+;
+}
+'
+Rejects
+SDP
+munging
+between
+createOffer
+and
+setLocalDescription
+'
+)
+;
+/
+/
+If
+type
+is
+"
+answer
+"
+or
+"
+pranswer
+"
+and
+sdp
+is
+not
+the
+empty
+string
+and
+not
+equal
+to
+/
+/
+connection
+.
+[
+[
+LastCreatedAnswer
+]
+]
+then
+return
+a
+promise
+rejected
+with
+a
+/
+/
+newly
+created
+InvalidModificationError
+and
+abort
+these
+steps
+.
+promise_test
+(
+async
+t
+=
+>
+{
+const
+pc
+=
+new
+RTCPeerConnection
+(
+)
+;
+t
+.
+add_cleanup
+(
+(
+)
+=
+>
+pc
+.
+close
+(
+)
+)
+;
+await
+pc
+.
+setRemoteDescription
+(
+{
+type
+:
+'
+offer
+'
+sdp
+}
+)
+;
+const
+answer
+=
+await
+pc
+.
+createAnswer
+(
+)
+;
+return
+promise_rejects_dom
+(
+t
+'
+InvalidModificationError
+'
+pc
+.
+setLocalDescription
+(
+{
+type
+:
+'
+answer
+'
+sdp
+:
+answer
+.
+sdp
++
+'
+a
+=
+munging
+-
+is
+-
+not
+-
+good
+\
+r
+\
+n
+'
+}
+)
+)
+;
+}
+'
+Rejects
+SDP
+munging
+between
+createAnswer
+and
+setLocalDescription
+'
+)
+;
+<
+/
+script
+>