Invalidate all extensions contexts on shutdown
Invalidate all extensions contexts on shutdown

BUG=584716
R=rdevlin.cronin@chromium.org,yzshen@chromium.org

Review URL: https://codereview.chromium.org/1702863004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#375983}

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