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

Review URL: https://codereview.chromium.org/874603002

Cr-Commit-Position: refs/heads/master@{#313010}
5 files changed