Revert of [Android] Stop hiding the RWHV layer subtree when hiding the widget (patchs...

Revert of [Android] Stop hiding the RWHV layer subtree when hiding the widget (patchset #12 id:330001 of https://codereview.chromium.org/1001573003/)

Reason for revert:
Speculative fix for blank display after cold startup.

Original issue's description:
> Reland "[Android] Preserve the front buffer when the activity is paused"
>
> This change was reverted in r322170 due to WebView breakage. The
> ApplicationStatus dependency has been made optional, allowing
> WebView to opt-out of its use.
>
> Original description: ----------------------------
>
> Currently, when an activity is stopped, we explicitly hide the
> foreground Tab. This is problematic, as current hiding semantics
> might clear the visual front buffer before the window is hidden.
> This in turn causes an unpleasant flickering during activity
> transitions, e.g., when backgrounding Chrome or locking the screen.
>
> Wire Activity onPause/onResume notifications to WindowAndroidObservers,
> allowing the foreground tab to preserve its front buffer while hiding
> its web content. If the tab is explicitly hidden, or the root window
> is lost, the front buffer will be cleared as usual.
>
> BUG=462752,434401
>
> Committed: https://crrev.com/7954daf991a2adda234dc2e886b2d1ddf0049221
> Cr-Commit-Position: refs/heads/master@{#322228}

TBR=sievers@chromium.org,dtrainor@chromium.org,tedchoc@chromium.org,piman@chromium.org,boliu@chromium.org,torne@chromium.org
BUG=481450,481115,434401

Review URL: https://codereview.chromium.org/1109863003

Cr-Commit-Position: refs/heads/master@{#327092}