Fix Assistant embedded UI dialog plate and thinking dot dimensions.

Currently the thinking dots are being clipped in embedded Assistant UI
and the dialog plate dimension is incorrect because it fails to account
for the padding around the horizontal seperator.

This CL:
- Increases the size of the progress indicator so that the thinking dots
  are not clipped.
- Modifies the vertical padding of the dialog plate so that it has the
  appearance of being 56dp tall even though a portion of that height is
  actually coming from the padding around the horizontal separator/
  progress indicator views.

Before: https://drive.google.com/open?id=1CSOiJoXIB0DSG7l3Mvf4Fj1-qQ9WwJCo
After: https://drive.google.com/open?id=1CL2K6kTGTJ7SCm13WDea8ytz_7-4iSO4

Bug: b:128857878
Change-Id: I0ab4bbce7883a12c1d92d1dcd0e80478c008453f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1529677
Commit-Queue: David Black <dmblack@google.com>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641797}
5 files changed