Nux Onboarding: get hard-coded module list from feature params instead.

In this CL, four FeatureParams were added.

These 2 are added for "os_win && google_chrome_build" when
kNuxOnboardingFeature is enabled:

kNuxOnboardingNewUserModules
kNuxOnboardingReturningUserModules

And 2 more are added for when the feature is force-enabled with
kNuxOnboardingForceEnabled on other platforms/non-branded build:

kNuxOnboardingForceEnabledNewUserModules
kNuxOnboardingForceEnabledReturningUserModules

Sample command line to test the changes:

./out/gn/chrome --user-data-dir=/tmp/debug_chrome_1 \
    --enable-features="NuxOnboardingForceEnabled<study" \
    --force-fieldtrials=study/g1 \
    --force-fieldtrial-params=study.g1:new-user-modules/nux-google-apps/returning-user-modules/nux-email

TBR=mpearson@chromium.org

Bug: 874153
Change-Id: I495e6492ee66ce20ec8bfad8743d20c9c55acf53
Reviewed-on: https://chromium-review.googlesource.com/c/1311659
Commit-Queue: Scott Chen <scottchen@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604748}
7 files changed