Fix skip_secondary_abi_for_cq

Adds some missing changes to support skip_secondary_abi_for_cq:
 - Adds manifest for 64bit only webview.
 - Creates 64bit-only test ar apk if skip_secondary_abi_for_cq.

Bug: 1217728
Change-Id: Ib7c233d681a6b1bf5266f4f11df555cf814387c0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3063580


Reviewed-by: Richard Coles <torne@chromium.org>
Commit-Queue: Mohamed Heikal <mheikal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#908143}