Restore main thread EnsureNSPRInit in the Linux ports.
Restore main thread EnsureNSPRInit in the Linux ports.

This got lost in the chimera on accident.

BUG=528468

Review URL: https://codereview.chromium.org/1332443002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#347573}

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