Implementing directional selection strategy in Blink.

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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 unifiedTextCheckerEnabled initial=defaultUnifiedTextCheckerEnabled
 
 # Some apps could have a default video poster if it is not set.
 defaultVideoPosterURL type=String
 
 smartInsertDeleteEnabled initial=defaultSmartInsertDeleteEnabled
 selectTrailingWhitespaceEnabled initial=defaultSelectTrailingWhitespaceEnabled
 
 selectionIncludesAltImageText initial=false
 
+selectionStrategy type=SelectionStrategy, initial=StrategyDefault
+
 ######## Settings used by Android WebView below ########
 
 useLegacyBackgroundSizeShorthandBehavior initial=false
 
 # This quirk is to maintain compatibility with Android apps built on
 # the Android SDK prior to and including version 18.
 # Presumably, this can be removed any time after 2015.
 # See http://crbug.com/282130.
 viewportMetaZeroValuesQuirk initial=false
 
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 useMobileViewportStyle initial=false, invalidate=ViewportRule
 
 # User style overrides for captions and subtitles
 textTrackBackgroundColor type=String
 textTrackFontFamily type=String
 textTrackFontStyle type=String
 textTrackFontVariant type=String
 textTrackTextColor type=String
 textTrackTextShadow type=String
 textTrackTextSize type=String