Fixed thread-unsafe use of gfx::Image in app shortcut creation.

Refactored web_app::ShortcutInfo so it is always passed via a scoped_ptr
(always having exactly one owner). This allows it to be safely passed
between threads without having a data race on the favicon image's
reference count.

Removed TSan suppression on ImageFamily.

BUG=364006

Review URL: https://codereview.chromium.org/1038573002

Cr-Commit-Position: refs/heads/master@{#324360}
18 files changed