Debugger: fix stepping when break points are deactivated.

Debugger: fix stepping when break points are deactivated.

The flag for deactivating break points also affects stepping, since both
are implemented via debug break slots. Fixing this by introducing a new
flag solely responsible for deactivating actual break points.

R=mvstanton@chromium.org
BUG=chromium:119800
LOG=N

Committed: https://crrev.com/4f7caf2f57449b1499646739a22e274afe5aa7e8
Cr-Commit-Position: refs/heads/master@{#31236}

[Yang, 2015-10-13 08:04:25]

The CQ bit was checked by yangguo@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-10-13 08:04:37]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1402913002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1402913002/20001

[commit-bot: I haz the power, 2015-10-13 08:27:00]

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

[commit-bot: I haz the power, 2015-10-13 08:27:01]

Dry run: This issue passed the CQ dry run.

[mvstanton, 2015-10-13 12:42:28]

lgtm

[Yang, 2015-10-13 12:42:39]

The CQ bit was checked by yangguo@chromium.org

[commit-bot: I haz the power, 2015-10-13 12:42:56]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1402913002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1402913002/20001

[commit-bot: I haz the power, 2015-10-13 12:44:13]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-13 12:44:35]

Patchset 2 (id:??) landed as
https://crrev.com/4f7caf2f57449b1499646739a22e274afe5aa7e8
Cr-Commit-Position: refs/heads/master@{#31236}