Don't assert that no incremental marking happened during a non-incremental GC

Don't assert that no incremental marking happened during a non-incremental GC

If a scavenge is triggered during the GC (via a weak callback or the GC
prologue/epilogue), and another mark-compact is triggered (via the same
unfortunate code path), we end up doing some incremental steps.

BUG=v8:4048
R=dcarney@chromium.org,hpayer@chromium.org
LOG=n

Committed: https://crrev.com/cc838be4b699c3f2324cc1850876ca8e8ae3a079
Cr-Commit-Position: refs/heads/master@{#27956}

[dcarney, 2015-04-21 09:28:23]

lgtm

[jochen (gone - plz use gerrit), 2015-04-21 09:29:23]

The CQ bit was checked by jochen@chromium.org

[commit-bot: I haz the power, 2015-04-21 09:29:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1096693011/1

[commit-bot: I haz the power, 2015-04-21 10:05:16]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-21 10:05:29]

Patchset 1 (id:??) landed as
https://crrev.com/cc838be4b699c3f2324cc1850876ca8e8ae3a079
Cr-Commit-Position: refs/heads/master@{#27956}