Support blink_logging_always_on in GN.
Support blink_logging_always_on in GN.

This is useful when you want logging in release builds.  It mirrors the GYP
option with the same name, defined in Source/build/features.gypi.

Review URL: https://codereview.chromium.org/1765573002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#379067}

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