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This change adds a pure 32-bit version of Monochrome, Trichrome and
Webview to the 64-bit build configuration. Building these targets
generates a product equivalent to building the targets on a 32-bit
config. However, by adding these, we have the option of building all
Monochrome and Trichrome products on a single 64-bit builder, and, we
share the compilation work (as opposed to the obsolete process of "APK
merging" parts from a 32-bit build into 64-bit products).

The targets added here are the public versions.

This change was originally reverted, because it exacerbated an unknown
dependency problem with Trichrome, causing problems on trybots. That
issue was fixed separately, meaning that these changes should be able to
re-land safely:

Revert: 8faa5fc4
Trichrome fix: d2a17895

It is being relanded with a follow-on change (that was also reverted),
updated to handle WebView bundles:

a2897b6b

Also added to this version is coverage of the new webview bundles.

TBR'ing torne and agrieve as they've already reviewed the original
changes.

TBR=torne@chromium.org, agrieve@chromium.org

Bug: 1027573
Change-Id: Ie1c9f042a7046505b081bfb9312e48ee8ee3b197
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1960575Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Reviewed-by: Richard Coles <torne@chromium.org>
Commit-Queue: Christopher Grant <cjgrant@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#723897}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1985527
Cr-Commit-Position: refs/heads/master@{#728525}