Rename TabManagerObserver to TabLifetimeObserver.

As part of the TabManager refactor, TabManager will be
renamed to LifetimeManager and will have no knowledge of
tabs / WebContents. It will only deal with generic
"LifetimeUnits". In that world, it doesn't make sense
to have a class name "TabManagerObserver" to observe
tab-specific events.

This CL renames TabManagerObserver to TabLifetimeObserver.
In a future CL, TabLifetimeObservers will no longer be
attached to TabManager. They will instead be attached
directly to TabLifetimeUnits.

TBR=lazyboy@chromium.org,

Bug: 723674
Change-Id: Id9ea1e6583eda3ba8d624c5d2162ba8b36d173f7
Reviewed-on: https://chromium-review.googlesource.com/726019
Reviewed-by: François Doray <fdoray@chromium.org>
Reviewed-by: Chris Hamilton <chrisha@chromium.org>
Commit-Queue: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#514489}
10 files changed