Rename propertyOffsetFor => offsetForPropertyNumber
https://bugs.webkit.org/show_bug.cgi?id=106685

Reviewed by Gavin Barraclough.

Since the argument is just a typedef and not an object, I wanted to clarify the meaning.

* runtime/PropertyMapHashTable.h:
(JSC::PropertyTable::nextOffset): Updated for rename.

* runtime/PropertyOffset.h:
(JSC::offsetForPropertyNumber): Renamed. Also changed some PropertyOffset variables
to plain ints, because they're not actually on the PropertyOffsets number line.

* runtime/Structure.cpp:
(JSC::Structure::flattenDictionaryStructure):
* runtime/Structure.h:
(JSC::Structure::lastValidOffset): Updated for rename.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@139481 268f45cc-cd09-0410-ab3c-d52691b4dbfc