Change generated code for substring not to bail out to runtime system.

Change generated code for substring not to bail out to runtime system.

There is no need to bail out to runtime system when creating sliced strings of external strings since the string content is unimportant.

Committed: http://code.google.com/p/v8/source/detail?r=10012

[Yang, 2011-11-16 17:26:13]

I should have kept the behavior in the runtime and that of the generated code in
sync back when I first implemented this. Please take a look.

[Rico, 2011-11-17 07:27:20]

LGTM

http://codereview.chromium.org/8513016/diff/2001/src/ia32/code-stubs-ia32.cc
File src/ia32/code-stubs-ia32.cc (right):

http://codereview.chromium.org/8513016/diff/2001/src/ia32/code-stubs-ia32.cc#...
src/ia32/code-stubs-ia32.cc:5980: STATIC_ASSERT(kIsIndirectStringMask ==
(kSlicedStringTag & kConsStringTag));
These two asserts and the following test is a bit hard to follow, please add a
comment explaining that if we don't have an indirect string we have either a
sequential or an external string (I, at least, had to go to objects.h to
convince myself of this)