Reland "Use backticks not vertical bars to denote variables in comments for /pc"

Original change's description:
> Revert "Use backticks not vertical bars to denote variables in comments for /pc"
>
> This reverts commit 37ee0f5e594dd772ec6d620b5e5ea8a751b684f0.
>
> Reason for revert: Revert in order to be able to revert https://webrtc-review.googlesource.com/c/src/+/225642
>
> Original change's description:
> > Use backticks not vertical bars to denote variables in comments for /pc
> >
> > Bug: webrtc:12338
> > Change-Id: I88cf10afa5fc810b95d2a585ab2e895dcc163b63
> > Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/226953
> > Reviewed-by: Harald Alvestrand <hta@webrtc.org>
> > Commit-Queue: Artem Titov <titovartem@webrtc.org>
> > Cr-Commit-Position: refs/heads/master@{#34575}
>
> TBR=hta@webrtc.org,titovartem@webrtc.org,webrtc-scoped@luci-project-accounts.iam.gserviceaccount.com
>
> Change-Id: I5eddd3a14e1f664bf831e5c294fbc4de5f6a88af
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: webrtc:12338
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227082
> Reviewed-by: Björn Terelius <terelius@webrtc.org>
> Commit-Queue: Björn Terelius <terelius@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#34577}

Bug: webrtc:12338
Change-Id: I96bd229b73613c162d11d75fa4f5934e1b4295c7
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227087
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34611}

pc/sdp_serializer_unittest.cc

diff --git a/pc/sdp_serializer_unittest.cc b/pc/sdp_serializer_unittest.cc
index b50f4f9..68d4c2a 100644
--- a/pc/sdp_serializer_unittest.cc
+++ b/pc/sdp_serializer_unittest.cc
@@ -96,8 +96,8 @@
 class SimulcastSdpSerializerTest : public TestWithParam<const char*> {
  public:
   // Runs a test for deserializing Simulcast.
-  // |str| - The serialized Simulcast to parse.
-  // |expected| - The expected output Simulcast to compare to.
+  // `str` - The serialized Simulcast to parse.
+  // `expected` - The expected output Simulcast to compare to.
   void TestDeserialization(const std::string& str,
                            const SimulcastDescription& expected) const {
     SdpSerializer deserializer;
@@ -107,8 +107,8 @@
   }
 
   // Runs a test for serializing Simulcast.
-  // |simulcast| - The Simulcast to serialize.
-  // |expected| - The expected output string to compare to.
+  // `simulcast` - The Simulcast to serialize.
+  // `expected` - The expected output string to compare to.
   void TestSerialization(const SimulcastDescription& simulcast,
                          const std::string& expected) const {
     SdpSerializer serializer;
@@ -280,8 +280,8 @@
 class RidDescriptionSdpSerializerTest : public TestWithParam<const char*> {
  public:
   // Runs a test for deserializing Rid Descriptions.
-  // |str| - The serialized Rid Description to parse.
-  // |expected| - The expected output RidDescription to compare to.
+  // `str` - The serialized Rid Description to parse.
+  // `expected` - The expected output RidDescription to compare to.
   void TestDeserialization(const std::string& str,
                            const RidDescription& expected) const {
     SdpSerializer deserializer;
@@ -291,8 +291,8 @@
   }
 
   // Runs a test for serializing RidDescriptions.
-  // |rid_description| - The RidDescription to serialize.
-  // |expected| - The expected output string to compare to.
+  // `rid_description` - The RidDescription to serialize.
+  // `expected` - The expected output string to compare to.
   void TestSerialization(const RidDescription& rid_description,
                          const std::string& expected) const {
     SdpSerializer serializer;