New parser mode for CSSOM @viewport descriptors.

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 26 matching lines @@
 
 class Document;
 
 enum CSSParserMode {
     CSSQuirksMode,
     CSSStrictMode,
     // SVG should always be in strict mode. For SVG attributes, the rules differ to strict sometimes.
     SVGAttributeMode,
     // User agent style sheet should always be in strict mode. Enables internal
     // only properties and values.
-    UASheetMode
+    UASheetMode,
+    // Parsing @viewport descriptors. Always strict.
+    ViewportMode
 };
 
 inline CSSParserMode strictToCSSParserMode(bool inStrictMode)
 {
     return inStrictMode ? CSSStrictMode : CSSQuirksMode;
 }
 
 inline bool isStrictParserMode(CSSParserMode cssParserMode)
 {
-    return cssParserMode == CSSStrictMode || cssParserMode == SVGAttributeMode || cssParserMode == UASheetMode;
+    return cssParserMode != CSSQuirksMode;
 }
 
 struct CSSParserContext {
     WTF_MAKE_FAST_ALLOCATED;
 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 isCSSCompositingEnabled;
     bool isCSSTouchActionEnabled;
     bool needsSiteSpecificQuirks;
 };
 
 bool operator==(const CSSParserContext&, const CSSParserContext&);
 inline bool operator!=(const CSSParserContext& a, const CSSParserContext& b) { return !(a == b); }
 
 const CSSParserContext& strictCSSParserContext();
 
 };
 
 #endif // CSSParserMode_h