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In summary, the changes revolve around making proguarding rules to keep foreign
symbols used by the module.

The following are the highlights:
- Investigate and add many missing "keep" rules to proguard file
- Fix R(esource) files to point to the appropriate location (base vs. module)
- Add build argument to build tab_ui as an async module
- Create file to keep proguarding rules that must be added manually
- Change proguard rule generation and add unit tests

Bug: 958026

Change-Id: I10904776d54a21bb292e2ef176750fdd338bcf40
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1627566
Commit-Queue: Fred Mello <fredmello@chromium.org>
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Reviewed-by: Tibor Goldschwendt <tiborg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#665328}