Fix static race in DatabaseAuthorizer's whitelistedFunctions.

The DatabaseAuthorizer is created on the main thread but used on
the database thread, we should use a thread safe static local to do
the init.

BUG=628480

Review-Url: https://codereview.chromium.org/2152173002
Cr-Commit-Position: refs/heads/master@{#405727}
1 file changed