GitLab

With this CL, TabLifecycleUnit is renamed to TabLifecycleUnitExternal
and it no longer inherits from LifecycleUnit. The name
"TabLifecycleUnitExternal" makes it clear that this interface is
exposed outside of chrome/browser/resource_coordinator/, and not
inheriting from LifecycleUnit restricts what's available outside
of chrome/browser/resource_coordinator/.

Also, this CL removes TabLifecycleUnitHolder.
TabLifecycleUnitExternal::FromWebContents will be implemented by
a map lookup in TabLifecycleUnitSource.

Bug: 775644
Change-Id: Ia8fa3b3a8c7f1d4289fc15f3f4d983192dda4db6
Reviewed-on: https://chromium-review.googlesource.com/788271
Commit-Queue: François Doray <fdoray@chromium.org>
Reviewed-by: Chris Hamilton <chrisha@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521352}