Use RELEASE_ASSERTs in WTF::initialize() and WTF::shutdown()
Use RELEASE_ASSERTs in WTF::initialize() and WTF::shutdown()

WTF doesn't support re-initialization. Make sure this in production.

BUG=514141

Review URL: https://codereview.chromium.org/1476183004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#361945}

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