Android: Let TabModelSelector close tab upon |onCloseContents|

Moves the call site of |TabModelSelector.closeTab| from
TabWebContentsDelegateAndroid to TabModelSelectorImpl in its
TabObserver.

This is in preparation for splitting TabWebContentsDelegateAndroid
into two, each with distinct responsibility.

Bug: 960746
Change-Id: I9e6637c48bee39c1568b0d73dfd6a89cdbbdafd9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1570985
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661934}
2 files changed