Implements JS bindings for mojo core module.

Mojo core module API is defined in //mojo/public/c/system/core.h.
The current implementation for JS bindings is implemented in //mojo/edk/js
using gin. This new blink implementation will replace the gin-based
implementation.

BUG=647036

Review-Url: https://codereview.chromium.org/2400563002
Cr-Commit-Position: refs/heads/master@{#449070}
23 files changed