Merge pull request #253 from xuzhang/extension_update

Add XW_Extension_Permissions.h and XW_Extension_Runtime.h
[Extension] Fix build issue on size_t not declared

The error was introduced the patch "sync files from crosswalk to
t-e-c. The header file <sys/types.h> is forgot to added in t-e-c.
Also function pointer is wrongly used on the patch 88b8aa029d1699.