Convert Settings::rootLayerScrolls to RuntimeEnabledFeatures

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?
@@ skipping 89 matching lines @@
 
 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
-
 # Used in layout tests for gesture tap highlights. Makes the highlights square
 # (rather than rounded) to make it possible to reftest the results.
 mockGestureTapHighlightsEnabled initial=false
 
 shouldRespectImageOrientation initial=false
 
 # Limited use by features which behave differently depending on the input
 # devices available.  For example, the pointer and hover media queries.
 # Note that we need to be careful when basing behavior or UI on this -
 # just because a device is present doesn't mean the user cares about it
@@ skipping 286 matching lines @@
 useDefaultImageInterpolationQuality initial=false
 
 # Variant of the ParseHTMLOnMainThread experiment. One experiment immediately
 # tokenizes input bytes. The default is to tokenize with a post task.
 parseHTMLOnMainThreadSyncTokenize initial=false
 # Variant of the ParseHTMLOnMainThread experiment. This is designed to coalesce
 # TokenizedChunks when the experiment is running in threaded mode.
 parseHTMLOnMainThreadCoalesceChunks initial=false
 
 browserSideNavigationEnabled initial=false