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This lets the Chromium PDF viewer get it's ink resources from
chormeos/componeonts/media_app_ui/resources/prod/lib/ink which is
built internally and shipped into CrOS as part of the media app.
The resources themselves are bundled via grit in
chromeos_media_app_bundle_resources.h.

In doing so we add the BUILD flag enable_use_media_app_ink:
* if true, don't build third_party/ink and thus don't create
gen/third_party/ink/ink_resources.pak, instead get resources from
gen/chromeos/chromeos_media_app_bundle_resources.pak
* if false, do what TOT currently does and build third_party/ink

This allows us to only ever build 1 set of ink resources into the
Chrome OS binary and avoid bloating the OS by ~ +2.4MB.
See size increase in
http://b/170161460#comment18 for more context.

This change also updates the externs of the ink library which works
with new ink resources and also the older ink resources
(third_party/ink/build) checked into TOT.

Regression tested with various builds of TOT, new ink resources & TOT
and new ink resources & this cl for the resource plumbing
(grd, flags etc) see regression testing in
http://b/170161460#comment18 for more context.

Note:
* currently enable_use_media_app_ink is just =
enable_cros_media_app but that might change.
* linux-chromeos-chrome trybot will fail until http://cl/347557653
lands and rolls into chromium. There is some time between
http://cl/347557653 rolling in and this cl landing which may mean the
OS is bloated with 2 copies of ink resources but this should be ok as
long as this is done before branch and in reality they will land in
O(day) time.

Bug: b/170161460, 1150244
Change-Id: I8e01ce9863dd00bcbab7b322ad3cf33c1424ec6f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2542926Reviewed-by: David Lei <dlei@google.com>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Bugs Nash <bugsnash@chromium.org>
Commit-Queue: David Lei <dlei@google.com>
Cr-Commit-Position: refs/heads/master@{#837450}