Use backticks not vertical bars to denote variables in comments for /api

Bug: webrtc:12338
Change-Id: Ib97b2c3d64dbd895f261ffa76a2e885bd934a87f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/226940
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34554}
diff --git a/api/frame_transformer_interface.h b/api/frame_transformer_interface.h
index 2cfe6ed..ab56f04 100644
--- a/api/frame_transformer_interface.h
+++ b/api/frame_transformer_interface.h
@@ -30,7 +30,7 @@
   // method call.
   virtual rtc::ArrayView<const uint8_t> GetData() const = 0;
 
-  // Copies |data| into the owned frame payload data.
+  // Copies `data` into the owned frame payload data.
   virtual void SetData(rtc::ArrayView<const uint8_t> data) = 0;
 
   virtual uint32_t GetTimestamp() const = 0;
@@ -78,7 +78,7 @@
 // the TransformedFrameCallback interface (see above).
 class FrameTransformerInterface : public rtc::RefCountInterface {
  public:
-  // Transforms |frame| using the implementing class' processing logic.
+  // Transforms `frame` using the implementing class' processing logic.
   virtual void Transform(
       std::unique_ptr<TransformableFrameInterface> transformable_frame) = 0;