Clarify Beacon transmission limit checking.

third_party/WebKit/Source/core/frame/Settings.json5

 {
   // Defines properties which are available on the Settings object.
   //
   // Please think carefully before adding a new Setting.  Some questions to
   // consider are:
   // - Should this be a RuntimeEnabledFeature instead? Settings are for things
   //   which we support either values of at runtime.  Features are set at renderer
   //   process startup and are never changed. Features also tend to be set to a
   //   value based on the platform or the stability of the code in question, where
   //   as settings both codepaths need to be stable.
@@ skipping 593 matching lines @@
       initial: "1.0",
       invalidate: "TextAutosizing",
       type: "double",
     },
 
     // This value indicates the maximum number of bytes a document is allowed to
     // transmit in Beacons (via navigator.sendBeacon()) -- Beacons are intended to be
     // smaller payloads transmitted as a page is unloading, not a general (one-way)
     // network transmission API. The spec <https://w3c.github.io/beacon/> does not
     // proscribe an upper limit, but allows for it -- the underlying API will return
-    // 'false' in that case.
+    // 'false' in that case. If the value is set to a negative value, no limit
+    // will be imposed.
     {
       name: "maxBeaconTransmission",
       initial: 65536,
       type: "int",
     },
 
     // This value is set to false if the platform does not support fullscreen.
     // When set to false all the requests to enter fullscreen will return an error
     // (fullscreenerror or webkitfullscreenerror) as specified in the standard:
     // http://fullscreen.spec.whatwg.org///dom-element-requestfullscreen
@@ skipping 294 matching lines @@
     },
 
     // Whether Blink should show media controls when `controls` attribute is used.
     {
       name: "mediaControlsEnabled",
       initial: true,
       invalidate: "MediaControls",
     },
   ],
 }