Add constants for X-Forwarded-Host and X-Forwarded-Port to HttpHeaders.
Add constants for X-Forwarded-Host and X-Forwarded-Port to HttpHeaders.

See https://github.com/google/guava/issues/2430
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rgoldberg/guava,google/guava,typetools/guava,Xaerxess/guava,google/guava,typetools/guava,berndhopp/guava,EdwardLee03/guava,berndhopp/guava,google/guava,EdwardLee03/guava,Xaerxess/guava,jakubmalek/guava,tli2/guava,xasx/guava,mosoft521/guava,xasx/guava,DavesMan/guava,mosoft521/guava,jakubmalek/guava,tli2/guava,mosoft521/guava,DavesMan/guava,rgoldberg/guava