Turn on DCHECKs and other debugging code if dcheck_always_on is 1

Turn on DCHECKs and other debugging code if dcheck_always_on is 1

When compiling with the macro DCHECK_ALWAYS_ON defined, DCHECKs and
supporting code gets compiled and enabled.

This increases test coverage for chromium release buildbots

BUG=v8:3731
R=jkummerow@chromium.org
LOG=y

[jochen (gone - plz use gerrit), 2014-12-03 16:21:33]

+kbr fyi

[Jakob Kummerow, 2014-12-04 08:59:46]

LGTM with nits.

Please also update the CL description -- there is no macro "DCHECK_ALWAYS_ON".

It's a bit sad that our own test suite doesn't pass with dcheck_always_on=1, but
the only solution I can think of is so ugly that I don't like it much either:
add yet another flag to the test driver, and define special test expectations. I
guess we'll just stick with running tests in good ol' release and (opt)debug
modes.

https://codereview.chromium.org/760213005/diff/20001/src/api.cc
File src/api.cc (right):

https://codereview.chromium.org/760213005/diff/20001/src/api.cc#newcode344
src/api.cc:344: #endif  // DEBUG
nit: s/DEBUG/VERIFY_HEAP/, again below

https://codereview.chromium.org/760213005/diff/20001/src/objects.h
File src/objects.h (right):

https://codereview.chromium.org/760213005/diff/20001/src/objects.h#newcode3081
src/objects.h:3081: #ifdef DEBUG
join this with the above block please

[jochen (gone - plz use gerrit), 2014-12-05 11:37:37]

The CQ bit was checked by jochen@chromium.org

[commit-bot: I haz the power, 2014-12-05 11:38:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/760213005/60001

[jochen (gone - plz use gerrit), 2014-12-05 12:00:05]

The CQ bit was unchecked by jochen@chromium.org

[jochen (gone - plz use gerrit), 2014-12-05 12:20:46]

The CQ bit was checked by jochen@chromium.org

[commit-bot: I haz the power, 2014-12-05 12:21:53]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/760213005/60001

[commit-bot: I haz the power, 2014-12-05 13:03:19]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-12-05 13:03:20]

Try jobs failed on following builders:
  v8_linux_arm64_rel on tryserver.v8
(http://build.chromium.org/p/tryserver.v8/builders/v8_linux_arm64_rel/builds/1587)

[jochen (gone - plz use gerrit), 2014-12-05 13:41:30]

The CQ bit was checked by jochen@chromium.org

[commit-bot: I haz the power, 2014-12-05 13:42:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/760213005/60001

[commit-bot: I haz the power, 2014-12-05 14:04:53]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-12-05 14:04:53]

Try jobs failed on following builders:
  v8_linux_arm64_rel on tryserver.v8
(http://build.chromium.org/p/tryserver.v8/builders/v8_linux_arm64_rel/builds/1591)

[jochen (gone - plz use gerrit), 2014-12-05 14:41:13]

The CQ bit was checked by jochen@chromium.org

[commit-bot: I haz the power, 2014-12-05 14:42:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/760213005/100001

[jochen (gone - plz use gerrit), 2014-12-05 14:46:34]

The CQ bit was unchecked by jochen@chromium.org

[jochen (gone - plz use gerrit), 2014-12-05 14:46:45]

Patchset #6 (id:100001) has been deleted

[jochen (gone - plz use gerrit), 2014-12-05 14:47:06]

Patchset #5 (id:80001) has been deleted

[jochen (gone - plz use gerrit), 2014-12-08 08:58:29]

The CQ bit was checked by jochen@chromium.org

[commit-bot: I haz the power, 2014-12-08 08:59:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/760213005/120001

[commit-bot: I haz the power, 2014-12-08 09:26:11]

Committed patchset #5 (id:120001)