[Offline indicator v2] Fix tablet CCT toolbar margin

Currently, top margin for the control container is calculated using
top_controls_height - tab_strip_and_toolbar_height (dimen). On tablet
CCTs, this may be negative since the tablet CCTs don't have a tab strip
while the tab_strip_and_toolbar_height always includes the tab strip
height on tablets.

A better way is to use the real view heights instead of dimens.

Bug: 1098716
Change-Id: I7428536b722df4489028115511a0c743665fd964
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2265176
Reviewed-by: Theresa  <twellington@chromium.org>
Reviewed-by: Matthew Jones <mdjones@chromium.org>
Commit-Queue: Sinan Sahin <sinansahin@google.com>
Cr-Commit-Position: refs/heads/master@{#782656}