[DNT] Destroy the animator when the WebContents is destroyed

Java could call TabAndroid::DestroyWebContents() on a visible
WebContents with its NativeView, layer and compositor still attached.

Fixed: 370494381
Change-Id: Ic8b290106a03710bdaa3d42be679896c4f5b4bbe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5900113
Commit-Queue: William Liu <liuwilliam@chromium.org>
Reviewed-by: Khushal Sagar <khushalsagar@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1362408}