Web setting for canvas2d msaa

Source/core/page/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 105 matching lines @@
 acceleratedCompositingForScrollableFramesEnabled initial=false
 compositedScrollingForFramesEnabled initial=false
 
 # 3D canvas (WebGL) support.
 webGLEnabled initial=false
 
 webGLErrorsToConsoleEnabled initial=true
 privilegedWebGLExtensionsEnabled initial=false
 accelerated2dCanvasEnabled initial=false
 antialiased2dCanvasEnabled initial=true
+accelerated2dCanvasMSAASampleCount type=int, initial=0
 
 # WebAudio support.
 webAudioEnabled initial=false
 
 fullScreenEnabled initial=false
 asynchronousSpellCheckingEnabled initial=false
 memoryInfoEnabled initial=false
 
 hyperlinkAuditingEnabled initial=false
 allowDisplayOfInsecureContent initial=true
@@ skipping 105 matching lines @@
 # behaves.  TODO(wjmaclean): link to design document.
 # crbug.com/304869 tracks removal.
 pinchVirtualViewportEnabled initial=false
 useSolidColorScrollbars initial=false
 
 mainFrameClipsContent initial=true
 
 # Enable decoration shadow nodes to test password genration feature
 # crbug.com/114092. This flag should not be enabled for production.
 passwordGenerationDecorationEnabled initial=false