Motivation:
If you test a header value providing a String, contains() returns false.
This is due to the implementation inherited from DefaultHeaders using
the JAVA_HASHER.
JAVA_HASHER.equals returns false because a is a String and b an
AsciiString.
Modifications:
DefaultHttp2Headers overrides contains and uses CASE_SENSITIVE_HASHER.
Result:
You can test a header value with any CharSequence implementation.
0db652277f