Add a comma delimited syntax parser and use it for Accept-CH

Source/platform/network/HTTPParsers.h

Index: Source/platform/network/HTTPParsers.h
diff --git a/Source/platform/network/HTTPParsers.h b/Source/platform/network/HTTPParsers.h
index cb82132baf423d16f7125c30f02a71afdb6f2c45..833d0829c9ff2d957716582a9364d5aac97e5796 100644
--- a/Source/platform/network/HTTPParsers.h
+++ b/Source/platform/network/HTTPParsers.h
@@ -33,7 +33,9 @@
 
 #include "platform/PlatformExport.h"
 #include "wtf/Forward.h"
+#include "wtf/HashSet.h"
 #include "wtf/Vector.h"
+#include "wtf/text/StringHash.h"
 
 namespace blink {
 
@@ -67,6 +69,8 @@ enum ReflectedXSSDisposition {
     BlockReflectedXSS
 };
 
+using CommaDelimitedHeaderSet = HashSet<String, CaseFoldingHash>;
+
 struct CacheControlHeader {
     bool parsed : 1;
     bool containsNoCache : 1;
@@ -97,6 +101,7 @@ PLATFORM_EXPORT ReflectedXSSDisposition parseXSSProtectionHeader(const String& h
 PLATFORM_EXPORT String extractReasonPhraseFromHTTPStatusLine(const String&);
 PLATFORM_EXPORT XFrameOptionsDisposition parseXFrameOptionsHeader(const String&);
 PLATFORM_EXPORT CacheControlHeader parseCacheControlDirectives(const AtomicString& cacheControlHeader, const AtomicString& pragmaHeader);
+PLATFORM_EXPORT void parseCommaDelimitedHeader(const String& headerValue, CommaDelimitedHeaderSet&);
 
 // -1 could be set to one of the return parameters to indicate the value is not specified.
 PLATFORM_EXPORT bool parseRange(const String&, long long& rangeOffset, long long& rangeEnd, long long& rangeSuffixLength);