Add forEach() to CSSVariablesMap

Source/core/core.gypi

 {
     'variables': {
         'deprecated_perl_core_idl_files': [
             'css/CSS.idl',
             'css/CSSCharsetRule.idl',
             'css/CSSFontFaceLoadEvent.idl',
             'css/CSSFontFaceRule.idl',
             'css/CSSHostRule.idl',
             'css/CSSImportRule.idl',
             'css/CSSMediaRule.idl',
@@ skipping 268 matching lines @@
             'xml/XMLHttpRequestProgressEvent.idl',
             'xml/XMLHttpRequestUpload.idl',
             'xml/XMLSerializer.idl',
             'xml/XPathEvaluator.idl',
             'xml/XPathExpression.idl',
             'xml/XPathNSResolver.idl',
             'xml/XPathResult.idl',
             'xml/XSLTProcessor.idl',
         ],
         'python_core_idl_files': [
+            'css/CSSVariablesMapForEachCallback.idl',
             'css/RGBColor.idl',
             'css/Rect.idl',
             'dom/ChildNode.idl',
             'dom/DocumentFullscreen.idl',
             'dom/ParentNode.idl',
             'dom/RequestAnimationFrameCallback.idl',
             'dom/StringCallback.idl',
             'html/VoidCallback.idl',
             'html/canvas/CanvasPattern.idl',
             'html/canvas/EXTFragDepth.idl',
@@ skipping 355 matching lines @@
             'css/CSSToStyleMap.cpp',
             'css/CSSToStyleMap.h',
             'css/CSSTransformValue.cpp',
             'css/CSSUnicodeRangeValue.cpp',
             'css/CSSUnicodeRangeValue.h',
             'css/CSSUnknownRule.h',
             'css/CSSValue.cpp',
             'css/CSSValueList.cpp',
             'css/CSSValuePool.cpp',
             'css/CSSValuePool.h',
+            'css/CSSVariablesIterator.h',
             'css/CSSVariablesMap.cpp',
             'css/CSSVariablesMap.h',
+            'css/CSSVariablesMapForEachCallback.h',
             'css/CSSVariableValue.h',
             'css/CSSViewportRule.h',
             'css/CSSViewportRule.cpp',
             'css/Counter.h',
             'css/DOMWindowCSS.cpp',
             'css/DOMWindowCSS.h',
             'css/DocumentRuleSets.cpp',
             'css/DocumentRuleSets.h',
             'css/ElementRuleCollector.cpp',
             'css/ElementRuleCollector.h',
@@ skipping 3116 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++"'
               }],
          ],
     }
 }