[Presentation API] Adding a flag to disable gesture check for starting presentations

third_party/WebKit/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?
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 # WebAudio support.
 webAudioEnabled initial=false
 
 hyperlinkAuditingEnabled initial=false
 allowDisplayOfInsecureContent initial=true
 allowRunningOfInsecureContent initial=true
 
 mediaControlsOverlayPlayButtonEnabled initial=false
 mediaPlaybackRequiresUserGesture initial=false
 
+presentationRequiresUserGesture initial=true
+
 scrollAnimatorEnabled initial=true
 
 # Used to disable threaded, compositor scrolling for testing purposes.
 # crbug.com/410974 tracks removal once alternative solutions for selective
 # main thread scrolling are supported.
 threadedScrollingEnabled initial=true, invalidate=Style
 
 # Handles frame-level scrolls via the root Layer instead of the FrameView.
 # crbug.com/417782 tracks enabling this by default.
 rootLayerScrolls initial=false
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 # Whether to disallow network fetches for parser blocking scripts in the main
 # frame inserted via document.write.
 disallowFetchForDocWrittenScriptsInMainFrame initial=false
 
 # The autoplay gesture override experiment is described in crbug.com/487345 .
 autoplayExperimentMode type=String, initial="off"
 
 # When DevTools is emulating mobile device, frame resize may mean device size has changed,
 # which in turn affects media queries.
 resizeIsDeviceSizeChange initial=false