Enable new mojo JS bindings in extensions blessed context.

This CL:
- Adds support to load extensions JS sources from gzipped resources, since the
  JS file for new mojo JS bindings is gzipped. The alternative is to change the
  JS file to uncompressed, which would increase Chrome size quite significantly.
  For example, adding ~132KB to resources.pak for Linux official build.
- Converts mimeHandlerPrivate to use new Mojo JS bindings.

BUG=699569, 718047

Change-Id: If485020558f607a1d2e81296476c60a20e7dd21b
Reviewed-on: https://chromium-review.googlesource.com/767649
Commit-Queue: Yuzhu Shen <yzshen@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516811}
14 files changed