Fix pop push optimization to work with partial snapshots (correct...

Fix pop push optimization to work with partial snapshots (correct
registration of external references in Proxy objects).
I moved the declaration of the two functions to stub-cache.h
because with all the types they use it's hard to declare them
anywhere else.  But the actual definition is still in runtime.cc
near to the place where they are used.

Committed: http://code.google.com/p/v8/source/detail?r=4231

[Kasper Lund, 2010-03-23 14:27:52]

LGTM!

http://codereview.chromium.org/1079012/diff/1/6
File src/assembler.h (right):

http://codereview.chromium.org/1079012/diff/1/6#newcode509
src/assembler.h:509: 
Intentional edit?