Pass custom root view to enable ListMenuButtons inside popup windows

This CL allows the user of `ListMenuButton` to pass a custom `RootView`
to the `AnchoredPopupWindow`. This is necessary when the
`ListMenuButton` is nested inside another popup window.

`AnchoredPopupWindow` passes its `mRootView` value to Android's
`PopupWindow::showAtLocation()` for Android to get the window token.
This value has to match the application's main window's
window token.

`ListMenuHost` used to pass `mView.getRootView()` to
`AnchoredPopupWindow`, which works fine when the `ListMenuButton` is
located inside the main application window. However, when the
`ListMenuButton` is inside another `PopupWindow`, the root view becomes
not the one of the main application window but the one of the popup
window. Therefore, we have to manually pass the correct root view of the main
application window when the `ListMenuButton` is nested.

Bug: 434061282
Change-Id: I64d97781a70a0ba7c98965d22dd20804f517194c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6963975
Reviewed-by: Wenyu Fu <wenyufu@chromium.org>
Commit-Queue: Masa Fujita <massan@google.com>
Cr-Commit-Position: refs/heads/main@{#1519204}