Refactor shadow rendering logic.

Source/core/core.gypi

 
 {
     'variables': {
         'core_idl_files': [
             'css/CSS.idl',
             'css/CSSCharsetRule.idl',
             'css/CSSFontFaceLoadEvent.idl',
             'css/CSSFontFaceRule.idl',
             'css/CSSHostRule.idl',
             'css/CSSImportRule.idl',
@@ skipping 2639 matching lines @@
             'platform/chromium/TraceEvent.h',
             'platform/chromium/VisitedLinksChromium.cpp',
             'platform/cocoa/KeyEventCocoa.h',
             'platform/cocoa/KeyEventCocoa.mm',
             'platform/graphics/ANGLEWebKitBridge.cpp',
             'platform/graphics/ANGLEWebKitBridge.h',
             'platform/graphics/BitmapImage.cpp',
             'platform/graphics/Color.cpp',
             'platform/graphics/CrossfadeGeneratedImage.cpp',
             'platform/graphics/CrossfadeGeneratedImage.h',
+            'platform/graphics/DrawLooper.cpp',
+            'platform/graphics/DrawLooper.h',
             'platform/graphics/Extensions3D.cpp',
             'platform/graphics/Extensions3D.h',
             'platform/graphics/Font.cpp',
             'platform/graphics/FontCache.cpp',
             'platform/graphics/FontData.cpp',
             'platform/graphics/FontDescription.cpp',
             'platform/graphics/FontFallbackList.cpp',
             'platform/graphics/FontFamily.cpp',
             'platform/graphics/FontFeatureSettings.cpp',
             'platform/graphics/FontFastPath.cpp',
@@ skipping 1005 matching lines @@
                 'bison_exe': 'bison',
                 # We specify a preprocess so it happens locally and won't get
                 # distributed to goma.
                 # FIXME: /usr/bin/gcc won't exist on OSX forever. We want to
                 # use /usr/bin/clang once we require Xcode 4.x.
                 'preprocessor': '--preprocessor "/usr/bin/gcc -E -P -x c++"'
               }],
          ],
     }
 }