Increase maxBeaconTransmission default to 64k bytes.

Source/core/frame/Settings.in

 # 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.
 # - How will you ensure test coverage of all relevant values of your setting?
@@ skipping 246 matching lines @@
 # websites that do not set an explicit viewport description.
 deviceScaleAdjustment type=double, initial=1.0, invalidate=TextAutosizing
 
 # 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://dvcs.w3.org/hg/webperf/raw-file/tip/specs/Beacon/Overview.html )
 # does not proscribe an upper limit, but allows for it -- the underlying
 # API will return 'false' in that case.
-maxBeaconTransmission type=int, initial=16384
+maxBeaconTransmission type=int, initial=65536
 
 # 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
 fullscreenSupported initial=true
 
 # FIXME: This is a temporary flag and should be removed once
 # the Android WebView framework supports fullscreen for non-media elements
 # (crbug.com/398485).
 # This value is set to false if the platform does not support fullscreen
 # for non-media elements. When set to true all the requests to enter fullscreen
 # on non-media elements will return an error.
 disallowFullscreenForNonMediaElements initial=false
 
 # V8 supports different types of caching. Used by V8 bindings.
 v8CacheOptions type=V8CacheOptions, initial=V8CacheOptionsOff