https://bugs.webkit.org/show_bug.cgi?id=113347

Patch by Benjamin Poulain <bpoulain@apple.com> on 2013-03-26
Reviewed by Geoffrey Garen.

The values zero and 0xffff have special values with the default HashTraits. Those values
are also valid values for UChar.

To avoid any table inconsitency, switch from UChar to uint32_t as the key type for
the WidthCache's single char map. The traits is also changed to allow zero as a normal
value.

This makes no space or time change over the previous code because:
-The struct KeyValuePair was already 64bits due to the ABI alignment restrictions on floats.
-The two hashes take the same number of instructions.

* platform/graphics/WidthCache.h:
(WidthCache):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@146954 268f45cc-cd09-0410-ab3c-d52691b4dbfc