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

third_party/WebKit/Source/core/css/BUILD.gn

 # 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.
 
 import("//third_party/WebKit/Source/core/core.gni")
 
 blink_core_sources("css") {
   split_count = 5
   sources = [
     "ActiveStyleSheets.cpp",
@@ skipping 296 matching lines @@
     "invalidation/StyleInvalidator.cpp",
     "invalidation/StyleInvalidator.h",
     "parser/CSSAtRuleID.cpp",
     "parser/CSSAtRuleID.h",
     "parser/CSSLazyParsingState.cpp",
     "parser/CSSLazyParsingState.h",
     "parser/CSSLazyPropertyParserImpl.cpp",
     "parser/CSSLazyPropertyParserImpl.h",
     "parser/CSSParser.cpp",
     "parser/CSSParser.h",
+    "parser/CSSParserContext.cpp",
+    "parser/CSSParserContext.h",
     "parser/CSSParserFastPaths.cpp",
     "parser/CSSParserFastPaths.h",
     "parser/CSSParserImpl.cpp",
     "parser/CSSParserImpl.h",
-    "parser/CSSParserMode.cpp",
     "parser/CSSParserMode.h",
     "parser/CSSParserObserverWrapper.cpp",
     "parser/CSSParserSelector.cpp",
     "parser/CSSParserSelector.h",
     "parser/CSSParserToken.cpp",
     "parser/CSSParserTokenRange.cpp",
     "parser/CSSParserTokenRange.h",
     "parser/CSSPropertyParser.cpp",
     "parser/CSSPropertyParser.h",
     "parser/CSSPropertyParserHelpers.cpp",
@@ skipping 58 matching lines @@
     "resolver/TransformBuilder.h",
     "resolver/ViewportStyleResolver.cpp",
     "resolver/ViewportStyleResolver.h",
   ]
 
   configs += [
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",
   ]
 }