Separate OnJNIOnLoad

Separate it into OnJNIOnLoadRegisterJNI() and OnJNIOnLoadInit(), so they
could be called by embedder when needed.

BUG=447393

Review URL: https://codereview.chromium.org/935413004

Cr-Commit-Position: refs/heads/master@{#317479}
18 files changed