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The manual layout just put one child view at the start and one in the
middle vertically. This CL removes the manual layout by introducing two
container views to be placed in equal size vertically.

BUG=1005568

Change-Id: Iae552da751d71175d3967deaf788a323221d0a1c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1884999
Commit-Queue: Wei Li <weili@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710578}