ash: Fix and re-enable TrayItemViewTest smoothness tests

A few issues fixed:
- `widget_` from `CreateFramelessTestWidget` has size 0 so UI
  changes are not actually drawn. And v3 does not count
  `did-not-produce-frame` as expected frames. So smoothness
  metrics are not reported. This is fixed by assigning a size
  to `widget_`.
- In the animation interruption tests, visibility animations
  are happening too quickly and end up as a no-op.
  For example, in HideSmoothnessMetricRecordedWhenHideInterruptsShow,
  Ui goes from `false` -> `true` -> `false`. But there is no actual
  opacity change because test does not wait for the intermediate show
  animation to progress a bit. This is fixed by waiting for
  opacity change before starting the 2nd animation.
- Wait for compositor to generate one frame before starting tests
  so that UI changes are picked up in time and generating smoothness
  metrics.

Re-enable the following TrayItemViewTest tests:
- TrayItemViewTest.SmoothnessMetricRecordedForHideAnimation
- TrayItemViewTest.SmoothnessMetricRecordedForShowAnimation
- TrayItemViewTest.HideSmoothnessMetricRecordedWhenHideInterruptsShow
- TrayItemViewTest.ShowSmoothnessMetricRecordedWhenShowInterruptsHide

Bug: chromium:41496872
Change-Id: I53829a5491f657875bac383f5b2fcfd7aa350280
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5292891
Reviewed-by: Andre Le <leandre@chromium.org>
Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1260582}