JSStackFrame Evisceration

This leaves sizeof(JSStackFrame) == 10 words (11 on 32-bit), but we only need to initialize 4 of those words on the common call path; the rest can be lazily (or never) initialized.

Members to remove

Sorted in estimated order of benefit / difficulty:

Task	Size (wks)	Assignee	Note
Xargc/argv/fun/script/thisv	3	lw	Requires StackSegment changes.
Xncode	3		Merge it with savedPC in method-jit. Requires building map HW PC --> bytecode (which we sortof already heave
scopeChain	.5
XdisplaySave	1	cdleary	Remove display optimization for great justice!
XhookData	.1	lw	Lazily initialize using JSStackFrame::flags. Included in bug 539144.
Xannotation	3	sayrer	Trivial if we can remove callers in nsScriptSecurityManager. Alas, that is not trivial, so this is going to take a while. For now, we lazily initialize which gives practically all the benefit.
XcallerVersion	.5	cdleary	Mostly the challenge is just understanding the actual use case.
XblockChain	1	wmmcloskey	A bit tricky
rval	1		Lazily initialize with a JSStackFrame::flags bit and avoid ever writing in the hot JM call/return paths.
Ximacpc	1	cdleary	Leave uninitialized in call path and use JSStackFrame::flags to indicate whether there is or is not an imacpc.