Generate shim headers when using system v8.

Generate shim headers when using system v8.

BUG=chromium:165264
Committed: http://code.google.com/p/v8/source/detail?r=13392

[Jakob Kummerow, 2013-01-09 09:58:15]

LGTM. I'll land this for you.

[Jakob Kummerow, 2013-01-09 10:57:19]

Uhm, no, scratch that. This CL breaks standalone V8 compilation, because
../build/shim_headers.gypi doesn't exist.

To repro: in a V8 checkout with this patch applied, run "make dependencies; make
out/Makefile.ia32" (or emerge Gentoo's dev-lang/v8 with this patch applied,
which should exhibit the same failure).

[Paweł Hajdan Jr., 2013-01-11 21:33:59]

PTAL

[Jakob Kummerow, 2013-01-14 12:07:46]

Generally LGTM, but I do have a question before landing this.

https://chromiumcodereview.appspot.com/11642006/diff/5001/tools/gyp/v8.gyp
File tools/gyp/v8.gyp (right):

https://chromiumcodereview.appspot.com/11642006/diff/5001/tools/gyp/v8.gyp#ne...
tools/gyp/v8.gyp:1005: 'variables': {
I get that when copy-pasting, it's good to avoid having to manually adapt the
pasted version, but: duplicate 'variables' sections? Are you sure this works as
intended?

[Paweł Hajdan Jr., 2013-01-14 18:43:44]

Oh, thank you for catching possible issues. I've done more testing for
use_system_v8=1 case, and indeed I had to fix a few things. Done now.

I intend to de-deuplicate this nicely with some changes gyp-side, but shipping
this to M26 if possible would be also cool.

[Jakob Kummerow, 2013-01-15 12:35:05]

OK, I'll land patch set 3.