Initial implementation of display list backed 2D canvases

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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 # Number of pixels below which 2D canvas is rendered in software
 # even if hardware acceleration is enabled.
 # Hardware acceleration is useful for large canvases where it can avoid the
 # pixel bandwidth between the CPU and GPU. But GPU acceleration comes at
 # a price - extra back-buffer and texture copy. Small canvases are also
 # widely used for stylized fonts. Anti-aliasing text in hardware at that
 # scale is generally slower. So below a certain size it is better to
 # draw canvas in software.
 minimumAccelerated2dCanvasSize type=int, initial=257*256
 
+displayList2dCanvasEnabled initial=false
+
 minimumFontSize type=int, initial=0, invalidate=Style
 minimumLogicalFontSize type=int, initial=0, invalidate=Style
 defaultFontSize type=int, initial=0, invalidate=Style
 defaultFixedFontSize type=int, initial=0, invalidate=Style
 
 editingBehaviorType type=EditingBehaviorType, initial=editingBehaviorTypeForPlatform()
 
 caretBrowsingEnabled initial=false
 localStorageEnabled initial=false
 allowUniversalAccessFromFileURLs initial=true
@@ skipping 203 matching lines @@
 
 # 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