Move painting code from RenderBoxModelObject into BoxPainter.

Source/core/core.gypi

 {
     'includes': [
       'core_generated.gypi',
     ],
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/Animation.idl',
             'animation/AnimationEffect.idl',
             'animation/AnimationPlayer.idl',
@@ skipping 1466 matching lines @@
             'page/WindowFeatures.cpp',
             'page/WindowFocusAllowedIndicator.cpp',
             'page/scrolling/ScrollingConstraints.cpp',
             'page/scrolling/ScrollingConstraints.h',
             'page/scrolling/ScrollingCoordinator.cpp',
             'page/scrolling/ScrollingCoordinator.h',
             'paint/BoxDecorationData.h',
             'paint/BoxDecorationData.cpp',
             'paint/BoxPainter.cpp',
             'paint/BoxPainter.h',
+            'paint/BackgroundImageGeometry.h',
+            'paint/BackgroundImageGeometry.cpp',
             'plugins/DOMMimeType.cpp',
             'plugins/DOMMimeType.h',
             'plugins/DOMMimeTypeArray.cpp',
             'plugins/DOMMimeTypeArray.h',
             'plugins/DOMPlugin.cpp',
             'plugins/DOMPlugin.h',
             'plugins/DOMPluginArray.cpp',
             'plugins/DOMPluginArray.h',
             'plugins/PluginOcclusionSupport.cpp',
             'plugins/PluginOcclusionSupport.h',
@@ skipping 2012 matching lines @@
             'rendering/shapes/BoxShapeTest.cpp',
             'rendering/style/OutlineValueTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'streams/ReadableStreamTest.cpp',
             'testing/UnitTestHelpers.cpp',
             'testing/UnitTestHelpers.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }