Speed up charCodeAt on very large cons strings, by insisting on...

Speed up charCodeAt on very large cons strings, by insisting on
flattening the strings and not trying too hard to traverse a big
cons tree from generated code.

Committed: http://code.google.com/p/v8/source/detail?r=3317

[Lasse Reichstein, 2009-11-17 10:08:20]

LGTM

http://codereview.chromium.org/402008/diff/1/4
File src/x64/codegen-x64.cc (right):

http://codereview.chromium.org/402008/diff/1/4#newcode3785
Line 3785: __ CompareRoot(temp.reg(), Heap::kEmptyStringRootIndex);
Is a memory read really more efficient than an extra opcode that loads the value
as a constant?