Introduce a gyp variable to control whether or not slow dchecks are on

Introduce a gyp variable to control whether or not slow dchecks are on

The default for the various debug modes doesn't change.

In a follow-up, OptDebug1 and OptDebug2 will be merged

R=machenbach@chromium.org
LOG=y
BUG=none

Committed: https://crrev.com/77e3e48ee23cccc990f82e1e744da2ad045002f1
Cr-Commit-Position: refs/heads/master@{#26015}

[dcarney, 2015-01-09 16:00:05]

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

[dcarney, 2015-01-09 16:00:05]

The CQ bit was checked by dcarney@chromium.org

[dcarney, 2015-01-09 16:00:05]

lgtm

[commit-bot: I haz the power, 2015-01-09 16:01:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/846653002/1

[commit-bot: I haz the power, 2015-01-09 16:25:44]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-09 16:26:03]

Patchset 1 (id:??) landed as
https://crrev.com/77e3e48ee23cccc990f82e1e744da2ad045002f1
Cr-Commit-Position: refs/heads/master@{#26015}

[Michael Achenbach, 2015-01-09 16:45:18]

lgtm