GitLab

For go/mustash we have to use mojo interfaces to communicate between
the ash process and chrome browser. Add a mojo method to show the
dialog.

Migrate code from SystemTrayDelegateChromeOS (deprecated and doesn't
exist in mash) and ChromeShellClient (also doesn't exist in mash)
into SessionControllerClient.

This helps consolidate more session-related code into
SessionControllerClient and reduce the size of SystemTrayDelegate.

TBR=oshima@chromium.org

Bug: 647412
Test: existing ash and chrome tests
Change-Id: I1f65f43a4fe668095325ad20c8dc0c201f706321
Reviewed-on: https://chromium-review.googlesource.com/557935Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#485334}