isLineExecutable() very slow.

Just a little tidbit from Firebug experience:

jsdIScript
http://www.xulplanet.com/references/xpcomref/ifaces/jsdIScript.html
has a method,
PRBool isLineExecutable ( PRUint32 line , PRUint32 pcmap )

Based on some very informal measurements I found that it takes about 1ms 
per line to call this method. When you apply that to 40k lines, not much 
goes on for while.

I don't know if this is intrinsic or just because of crossing in and out 
of C++ but it would be good to understand so we can create a faster next 
gen API.  For example we could replace this with

Array<int> executableLines(pcmap);

for most applications.

jjb