Remove CSS regions support, keeping a bare minimum to support "region-based" multicol.

Source/core/core.gypi

 {
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/Animation.idl',
             'animation/Player.idl',
             'animation/TimedItem.idl',
             'animation/Timeline.idl',
             'clipboard/Clipboard.idl',
             'clipboard/DataTransferItem.idl',
@@ skipping 27 matching lines @@
             'css/MediaList.idl',
             'css/MediaQueryList.idl',
             'css/RGBColor.idl',
             'css/Rect.idl',
             'css/StyleMedia.idl',
             'css/StyleSheet.idl',
             'css/StyleSheetList.idl',
             'css/WebKitCSSFilterRule.idl',
             'css/WebKitCSSFilterValue.idl',
             'css/WebKitCSSMatrix.idl',
-            'css/WebKitCSSRegionRule.idl',
             'css/WebKitCSSTransformValue.idl',
             'dom/Attr.idl',
             'dom/CDATASection.idl',
             'dom/CharacterData.idl',
             'dom/ClientRect.idl',
             'dom/ClientRectList.idl',
             'dom/Comment.idl',
             'dom/DOMError.idl',
             'dom/DOMException.idl',
             'dom/DOMImplementation.idl',
@@ skipping 18 matching lines @@
             'dom/ProcessingInstruction.idl',
             'dom/Promise.idl',
             'dom/Range.idl',
             'dom/RequestAnimationFrameCallback.idl',
             'dom/StringCallback.idl',
             'dom/Text.idl',
             'dom/Touch.idl',
             'dom/TouchList.idl',
             'dom/TreeWalker.idl',
             'dom/URL.idl',
-            'dom/WebKitNamedFlow.idl',
-            'dom/WebKitNamedFlowCollection.idl',
             'dom/XMLDocument.idl',
             'dom/shadow/ShadowRoot.idl',
             'events/AutocompleteErrorEvent.idl',
             'events/BeforeLoadEvent.idl',
             'events/BeforeUnloadEvent.idl',
             'events/CompositionEvent.idl',
             'events/CustomEvent.idl',
             'events/ErrorEvent.idl',
             'events/Event.idl',
             'events/EventTarget.idl',
@@ skipping 608 matching lines @@
             'css/CSSPageRule.h',
             'css/parser/BisonCSSParser.h',
             'css/CSSParserMode.cpp',
             'css/CSSParserMode.h',
             'css/CSSParserValues.cpp',
             'css/CSSPrimitiveValue.cpp',
             'css/CSSPrimitiveValueMappings.h',
             'css/CSSProperty.cpp',
             'css/CSSPropertySourceData.cpp',
             'css/CSSReflectValue.cpp',
-            'css/CSSRegionRule.cpp',
-            'css/CSSRegionRule.h',
             'css/CSSRule.cpp',
             'css/CSSRule.h',
             'css/CSSRuleList.cpp',
             'css/CSSRuleList.h',
             'css/CSSSVGDocumentValue.cpp',
             'css/CSSSVGDocumentValue.h',
             'css/CSSSegmentedFontFace.cpp',
             'css/CSSSegmentedFontFace.h',
             'css/CSSSelector.cpp',
             'css/CSSSelectorList.cpp',
@@ skipping 742 matching lines @@
             'rendering/RenderMenuList.cpp',
             'rendering/RenderMenuList.h',
             'rendering/RenderMeter.cpp',
             'rendering/RenderMeter.h',
             'rendering/RenderMultiColumnBlock.cpp',
             'rendering/RenderMultiColumnBlock.h',
             'rendering/RenderMultiColumnFlowThread.cpp',
             'rendering/RenderMultiColumnFlowThread.h',
             'rendering/RenderMultiColumnSet.cpp',
             'rendering/RenderMultiColumnSet.h',
-            'rendering/RenderNamedFlowFragment.cpp',
-            'rendering/RenderNamedFlowFragment.h',
-            'rendering/RenderNamedFlowThread.cpp',
-            'rendering/RenderNamedFlowThread.h',
             'rendering/RenderObject.cpp',
             'rendering/RenderObjectChildList.cpp',
             'rendering/RenderPart.cpp',
             'rendering/RenderProgress.cpp',
             'rendering/RenderProgress.h',
             'rendering/RenderQuote.cpp',
             'rendering/RenderQuote.h',
             'rendering/RenderRegion.cpp',
             'rendering/RenderRegion.h',
             'rendering/RenderRegionSet.cpp',
@@ skipping 379 matching lines @@
             'dom/DocumentStyleSheetCollection.cpp',
             'dom/DocumentStyleSheetCollection.h',
             'dom/DocumentStyleSheetCollector.cpp',
             'dom/DocumentStyleSheetCollector.h',
             'dom/DocumentType.cpp',
             'dom/DOMError.cpp',
             'dom/DOMError.h',
             'dom/DOMException.cpp',
             'dom/DOMException.h',
             'dom/DOMImplementation.cpp',
-            'dom/DOMNamedFlowCollection.cpp',
-            'dom/DOMNamedFlowCollection.h',
             'dom/DOMSettableTokenList.cpp',
             'dom/DOMSettableTokenList.h',
             'dom/DOMStringList.cpp',
             'dom/DOMStringList.h',
             'dom/DOMStringMap.cpp',
             'dom/DOMStringMap.h',
             'dom/DOMTokenList.cpp',
             'dom/DOMTokenList.h',
             'dom/DOMURL.cpp',
             'dom/DOMURL.h',
@@ skipping 35 matching lines @@
             'dom/Microtask.h',
             'dom/MutationCallback.h',
             'dom/MutationObserver.cpp',
             'dom/MutationObserver.h',
             'dom/MutationObserverInterestGroup.cpp',
             'dom/MutationObserverInterestGroup.h',
             'dom/MutationObserverRegistration.cpp',
             'dom/MutationObserverRegistration.h',
             'dom/MutationRecord.cpp',
             'dom/MutationRecord.h',
-            'dom/NamedFlow.cpp',
-            'dom/NamedFlow.h',
-            'dom/NamedFlowCollection.cpp',
-            'dom/NamedFlowCollection.h',
             'dom/NamedNodeMap.cpp',
             'dom/NamedNodesCollection.cpp',
             'dom/NamedNodesCollection.h',
             'dom/NameNodeList.cpp',
             'dom/NameNodeList.h',
             'dom/Node.cpp',
             'dom/NodeChildRemovalTracker.h',
             'dom/NodeChildRemovalTracker.cpp',
             'dom/NodeFilter.cpp',
             'dom/NodeFilter.h',
@@ skipping 1303 matching lines @@
             'html/parser/HTMLParserThreadTest.cpp',
             'html/track/vtt/BufferedLineReaderTest.cpp',
             'html/track/vtt/VTTScannerTest.cpp',
             'rendering/RenderOverflowTest.cpp',
             'rendering/shapes/BoxShapeTest.cpp',
             'testing/UnitTestHelpers.cpp',
             'testing/UnitTestHelpers.h',
         ],
     }
 }