Allow mmap encoded data replacement for WOFF fonts.

Allow mmap encoded data replacement for WOFF fonts.
<https://webkit.org/b/127737>

We always have to convert WOFF fonts to SFNT format. This happens
in a separate buffer from the CachedFont's internal resource buffer.
Because of this, there's no need to protect the original buffer from
mmap replacement.

With this change, WOFF web fonts are no longer duplicated between
the network and web processes.

Reviewed by Brady Eidson.

* loader/cache/CachedFont.cpp:
(WebCore::CachedFont::CachedFont):
(WebCore::CachedFont::ensureCustomFontData):
(WebCore::CachedFont::mayTryReplaceEncodedData):
* loader/cache/CachedFont.h:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@162897 268f45cc-cd09-0410-ab3c-d52691b4dbfc