Initialize gFunctionMap from CoreInitializer

Before this CL, gFunctionMap init was racy, as it could be initialized from both BackgroundParserThread/CrRendererMain.
This CL ties the init to blink::initialize() to avoid the issue.

BUG=626493

Review-Url: https://codereview.chromium.org/2135083003
Cr-Commit-Position: refs/heads/master@{#404738}
3 files changed