Make it possible for downstream projects to easily set the default fill color

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 136 matching lines @@
 cookieEnabled initial=true
 navigateOnDragDrop initial=true
 DOMPasteAllowed initial=false
 
 allowCustomScrollbarInMainFrame initial=true
 webSecurityEnabled initial=true
 
 # Special keyboard navigation mode intented for platforms with no
 # proper mouse or touch support, such as a TV controller with a remote.
 spatialNavigationEnabled initial=false
+defaultBackgroundColor type=Color, initial=Color::white
 
 # This setting adds a means to enable/disable touch initiated drag & drop. If
 # enabled, the user can initiate drag using long press.
 # crbug.com/304894 tracks removal once it's been enabled on all platforms.
 touchDragDropEnabled initial=false
 
 unifiedTextCheckerEnabled initial=false
 
 # Some apps could have a default video poster if it is not set.
 defaultVideoPosterURL type=String
@@ skipping 241 matching lines @@
 # to enable it have been shipped.
 passiveListenerDefault type=PassiveListenerDefault, initial=PassiveListenerDefault::False
 
 # Use default interpolation quality to scale bitmap images if quality is not determined
 # in other ways. This can help us writing reftests containing scaled images.
 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