Always drain blocked modules log

Since it is possible for a module to be blocked even though the feature
is disabled, the class that drains the log of blocked modules is now
part of the ModuleDatabase and always initialized.

Also, the ModuleDatabase is now aware of blocked modules and they are
shown in the chrome://conflicts page.

Bug: 846953
Change-Id: I993a51571e4d4f630ab6852b54920598bad26ac3
Reviewed-on: https://chromium-review.googlesource.com/1141158
Commit-Queue: Patrick Monette <pmonette@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Bernhard Bauer <bauerb@chromium.org>
Reviewed-by: Chris Hamilton <chrisha@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576925}
18 files changed