RC: Pass the OnNonPersistentNotificationCreated signal to c/b/rc

This forwards the |kNonPersistentNotificationCreated| events received
in services/resource_coordinator/ to the page signal observer on the
browser side (c/b/rc). Non-persistent notifications are web
notifications created by a page, they require the page to be alive to
be created (persistent notifications are created by service workers and
don't rely on the page to be alive)

These events will be recorded in the local site characteristics
database in a further CL. We need to consider potential usage of
non-persistent web notifications before proactively discarding a tab to
make sure that we don't discard a tab that could try to communicate
with the user via non-persistent web notifications.

Bug: 773382
Change-Id: I0245cd4514541a2f70b547d5ce9fab0e633ddf94
Reviewed-on: https://chromium-review.googlesource.com/1068665
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Chris Hamilton <chrisha@chromium.org>
Commit-Queue: Sébastien Marchand <sebmarchand@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562539}

• chrome/browser/resource_coordinator/page_signal_receiver.cc[diff]
• chrome/browser/resource_coordinator/page_signal_receiver.h[diff]
• chrome/browser/resource_coordinator/tab_manager_resource_coordinator_signal_observer.cc[diff]
• chrome/browser/resource_coordinator/tab_manager_resource_coordinator_signal_observer.h[diff]
• services/resource_coordinator/observers/page_signal_generator_impl.cc[diff]
• services/resource_coordinator/observers/page_signal_generator_impl.h[diff]
• services/resource_coordinator/observers/page_signal_generator_impl_unittest.cc[diff]
• services/resource_coordinator/public/mojom/page_signal.mojom[diff]