Introduce a external allocation limit....

Introduce a external allocation limit.

If V8 is holding on to a lot of external memory, we attempt to clean
it up even if we do not get an allocation failure.  Since tiny V8
objects can hold on to a lot of external memory, we might run out of
external memory while waiting for a normal allocation failure.

Committed: http://code.google.com/p/v8/source/detail?r=2519

[Kevin Millikin (Chromium), 2009-07-22 09:55:45]

LGTM.  Could make it 8*semispace_size_ if you like that sort of thing (powers of
two).