MacViews: Use the ContrainedWindow animations for MODAL_TYPE_CHILD
WindowModal sheets get their animations from Cocoa (and modality is
enforced by Cocoa). The "Child" dialog type is used for
WebContents-modal dialogs and has a custom animation, now in
ui/base/cocoa. (For aura, window animations happen in ui/wm/core). So
for MacViews, these animations can fit at a similar level (i.e. outside
of chrome/browse/ui).
Use a nonblocking (UI-thread) animation for now. It simplifies things,
but complex dialogs might need some extra smarts to coordinate with the
compositor if performance isn't up to scratch on user hardware.
Cocoa animations can outlast the toolkit-views objects involved, so add
a test to cover these flows.
BUG=485854
Review URL: https://codereview.chromium.org/
1145373008
Cr-Commit-Position: refs/heads/master@{#332487}