NaCl: Simplify the plumbing for PPAPI's DevInterfacesEnabled flag

NaCl: Simplify the plumbing for PPAPI's DevInterfacesEnabled flag

There's no need for this flag to be sent from ppb_nacl_private_impl.cc
to plugin.cc and back again.  It can stay within
ppb_nacl_private_impl.cc.

This merges two error-handling checks in LaunchSelLdr().

BUG=239656
TEST=browser_tests

Committed: https://crrev.com/70e58ead2e061d1044b10a3781f9c21d3ed10e0c
Cr-Commit-Position: refs/heads/master@{#313010}

[Mark Seaborn, 2015-01-23 22:50:57]

mseaborn@chromium.org changed reviewers:
+ teravest@chromium.org

[teravest, 2015-01-24 02:40:33]

lgtm

[Mark Seaborn, 2015-01-24 05:15:59]

The CQ bit was checked by mseaborn@chromium.org

[commit-bot: I haz the power, 2015-01-24 05:16:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/874603002/1

[commit-bot: I haz the power, 2015-01-24 05:20:57]

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

[commit-bot: I haz the power, 2015-01-24 05:20:59]

Try jobs failed on following builders:
  chromium_presubmit on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)

Try jobs failed on following builders:
  chromium_presubmit on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)

[Mark Seaborn, 2015-01-24 05:33:20]

The CQ bit was checked by mseaborn@chromium.org

[commit-bot: I haz the power, 2015-01-24 05:33:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/874603002/20001

[commit-bot: I haz the power, 2015-01-24 06:19:58]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-01-24 06:20:54]

Patchset 2 (id:??) landed as
https://crrev.com/70e58ead2e061d1044b10a3781f9c21d3ed10e0c
Cr-Commit-Position: refs/heads/master@{#313010}