Wait for sweeper threads only if we have to.

Wait for sweeper threads only if we have to, i.e. if we globally have to finish sweeping or if we have to allocate from a certain space.
BUG=
R=ulan@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=22156

[ulan, 2014-07-02 06:45:47]

https://codereview.chromium.org/361983003/diff/1/src/spaces.h
File src/spaces.h (right):

https://codereview.chromium.org/361983003/diff/1/src/spaces.h#newcode1997
src/spaces.h:1997: bool was_swept_concurrently_;
It seems to be uninitialized.

[Hannes Payer (out of office), 2014-07-02 07:00:52]

https://codereview.chromium.org/361983003/diff/1/src/spaces.h
File src/spaces.h (right):

https://codereview.chromium.org/361983003/diff/1/src/spaces.h#newcode1997
src/spaces.h:1997: bool was_swept_concurrently_;
On 2014/07/02 06:45:47, ulan wrote:
> It seems to be uninitialized.

Done.

[Hannes Payer (out of office), 2014-07-02 07:02:53]

https://codereview.chromium.org/361983003/diff/20001/src/spaces.h
File src/spaces.h (right):

https://codereview.chromium.org/361983003/diff/20001/src/spaces.h#newcode1993
src/spaces.h:1993: // an non-iterable or iterable heap, respectively.
Actually, we could just store the sweeper type itself. I will do that.

[Hannes Payer (out of office), 2014-07-02 07:52:38]

We cannot have the Space <-> MarkCompactCollector::SweeperType. Can you please
have another look?

[ulan, 2014-07-02 08:02:03]

lgtm

[Hannes Payer (out of office), 2014-07-02 12:33:19]

Committed patchset #3 manually as r22156 (presubmit successful).