add comments for the reference of image mimesniff

Author: Hajime-san

ext/canvas/op_create_image_bitmap.rs

@@ -179,9 +179,6 @@ See: https://developer.mozilla.org/en-US/docs/Web/API/Blob/type\n",
         }
         // return an error if the MIME type is not supported in the variable list of ImageTypePatternTable below
         // ext/web/01_mimesniff.js
-        //
-        // NOTE: Chromium supports AVIF
-        // https://source.chromium.org/chromium/chromium/src/+/ef3f4e4ed97079dc57861d1195fb2389483bc195:third_party/blink/renderer/platform/image-decoders/image_decoder.cc;l=311
         x => {
           return Err(
             DOMExceptionInvalidStateError::new(

ext/web/01_mimesniff.js

@@ -395,6 +395,10 @@ const ImageTypePatternTable = [
 
 /**
  * Ref: https://mimesniff.spec.whatwg.org/#image-type-pattern-matching-algorithm
+ * NOTE: Some browsers have implementation-defined image formats.
+ * For example, The AVIF image format is supported by all browsers today.
+ * However, the standardization seems to have hard going.
+ * See: https://github.com/whatwg/mimesniff/issues/143
  * @param {Uint8Array} input
  * @returns {string | undefined}
  */