This is straightforward, with only two notable things.
- `#include "nsXPIDLString.h" is replaced with `#include "nsString.h"`
throughout, because all nsXPIDLString.h did was include nsString.h. The
exception is for files which already include nsString.h, in which case the
patch just removes the nsXPIDLString.h inclusion.
- The patch removes the |xpidl_string| gtest, but improves the |voided| test to
cover some of its ground, e.g. testing Adopt(nullptr).
In all of these cases the fixed buffer has the same lifetime as the string
object, so we can use nsAuto[C]String for simplicity.
For the 128-length ones in dom/xul/ I just switched to the default of 64 for
simplicity, because the choice of 128 didn't seem that important. (These code
paths weren't hit when I started the browser and opened a few sites.)
Finally, the patch also changes LoggingIdString to use
nsAutoCStringN<NSID_LENGTH>, similar to NullPrincipalURI.
