Remove CSS_REGIONS compile flag from Blink.

Source/core/css/CSSParserMode.h

 /*
  * Copyright (C) 2012 Adobe Systems Incorporated. All rights reserved.
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above
  *    copyright notice, this list of conditions and the following
@@ skipping 47 matching lines @@
 public:
     CSSParserContext(CSSParserMode, const KURL& baseURL = KURL());
     CSSParserContext(Document*, const KURL& baseURL = KURL(), const String& charset = emptyString());
 
     KURL baseURL;
     String charset;
     CSSParserMode mode;
     bool isHTMLDocument;
     bool isCSSCustomFilterEnabled;
     bool isCSSStickyPositionEnabled;
-    bool isCSSRegionsEnabled;
     bool isCSSCompositingEnabled;
     bool isCSSGridLayoutEnabled;
     bool isCSSVariablesEnabled;
     bool needsSiteSpecificQuirks;
     RefPtr<Document> m_document;
 };
 
 bool operator==(const CSSParserContext&, const CSSParserContext&);
 inline bool operator!=(const CSSParserContext& a, const CSSParserContext& b) { return !(a == b); }
 
 const CSSParserContext& strictCSSParserContext();
 
 };
 
 #endif // CSSParserMode_h