Special case the "empty string" root so it doesn't constantly jump around

Special case the "empty string" root so it doesn't constantly jump around

BUG=none
R=hpayer@chromium.org
LOG=n

Committed: https://crrev.com/f56fb72f984a212e698c27799b5d10b9aace59db
Cr-Commit-Position: refs/heads/master@{#27736}

[Hannes Payer (out of office), 2015-04-10 08:49:01]

lgtm

[jochen (gone - plz use gerrit), 2015-04-10 09:07:22]

The CQ bit was checked by jochen@chromium.org

[commit-bot: I haz the power, 2015-04-10 09:07:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1075133002/20001

[Yang, 2015-04-10 09:23:36]

yangguo@chromium.org changed reviewers:
+ yangguo@chromium.org

[Yang, 2015-04-10 09:23:36]

https://codereview.chromium.org/1075133002/diff/20001/src/heap/heap.h
File src/heap/heap.h (right):

https://codereview.chromium.org/1075133002/diff/20001/src/heap/heap.h#newcode63
src/heap/heap.h:63: /* The roots above this line should be boring from a GC
point of view.    */ \
I think there was a reason there were only 32 items before this comment. I don't
remember what the reason was though.

[commit-bot: I haz the power, 2015-04-10 09:23:49]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-04-10 09:24:03]

Patchset 2 (id:??) landed as
https://crrev.com/f56fb72f984a212e698c27799b5d10b9aace59db
Cr-Commit-Position: refs/heads/master@{#27736}