Split the CSSParserContext class out of CSSParserMode into its own file.

third_party/WebKit/Source/core/css/properties/CSSPropertyAPI.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CSSPropertyAPI_h
 #define CSSPropertyAPI_h
 
 #include "core/CSSPropertyNames.h"
-#include "core/css/CSSValue.h"
-#include "core/css/parser/CSSParserMode.h"
-#include "core/css/parser/CSSParserTokenRange.h"
+#include "wtf/Allocator.h"
 
 namespace blink {
 
+class CSSValue;
+class CSSParserContext;
+class CSSParserTokenRange;
+
 // We will use this API to represent all functions used for property-specific
 // logic inside the blink style engine. All specific properties are subclasses
 // of CSSPropertyAPI.
 //
 // To add a new property using this API:
 // - Make a class that implements CSSPropertyAPI, and implement the static
 //   methods.
 // - Update the cssPropertyDescriptors array in CSSPropertyDescriptor.cpp to
 //   call GET_DESCRIPTOR(classname).
 //
 // To add new functions using this API:
 // - New functions and static variables can be added in this class. A default
 //   implementation of functions can optionally be provided.
 // - When adding new functions, also add them to GET_DESCRIPTOR, and the get()
 //   method in CSSPropertyDescriptors.cpp, and the descriptor struct in
 //   CSSPropertyDescriptor.h.
 class CSSPropertyAPI {
   STATIC_ONLY(CSSPropertyAPI);
 
  public:
   // Parses a single CSS property and returns the corresponding CSSValue. If the
   // input is invalid it returns nullptr.
   static const CSSValue* parseSingleValue(CSSParserTokenRange&,
                                           const CSSParserContext&);
 };
 
 }  // namespace blink
 
 #endif  // CSSPropertyAPI_h