Reland of Allow direct and indirect navigation values to be varied via field trial.

Reland of Allow direct and indirect navigation values to be varied via field trial. (patchset #1 id:1 of https://codereview.chromium.org/1322503002/ )

Reason for revert:
The revert didn't help.

Original issue's description:
> Revert of Allow direct and indirect navigation values to be varied via field trial. (patchset #3 id:60001 of https://codereview.chromium.org/1309803005/ )
>
> Reason for revert:
> Looks like this broke org.chromium.chrome.browser.banners.AppBannerManagerTest : http://build.chromium.org/p/chromium.linux/builders/Android%20Tests%20%28dbg%29/builds/29822
> http://build.chromium.org/p/chromium.linux/builders/Android%20Tests/builds/21895
>
> Original issue's description:
> > Allow direct and indirect navigation values to be varied via field trial.
> >
> > This CL allows the engagement scores assigned to direct and indirect
> > navigations to be varied via a field trial. It also makes method names
> > related to the setting of values in AppBannerSettingsHelper more
> > consistent.
> >
> > BUG=487519
> >
> > Committed: https://crrev.com/633bbe04d2525d7272a78d78f8e3fdd0abe4d5a2
> > Cr-Commit-Position: refs/heads/master@{#345729}
>
> TBR=benwells@chromium.org,dfalcantara@chromium.org,dominickn@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=487519
>
> Committed: https://crrev.com/22586e128b6861c2674025a836998e9ef59db51c
> Cr-Commit-Position: refs/heads/master@{#345793}

TBR=benwells@chromium.org,dfalcantara@chromium.org,dominickn@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=487519
Committed: https://crrev.com/23a2e942e6bcd0797761ad0e2f0a2be4f32ce238
Cr-Commit-Position: refs/heads/master@{#345811}

[Nico, 2015-08-27 06:27:29]

Created Reland of Allow direct and indirect navigation values to be varied via
field trial.

[commit-bot: I haz the power, 2015-08-27 06:27:36]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1314273004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1314273004/1

[commit-bot: I haz the power, 2015-08-27 06:28:06]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-27 06:28:51]

Patchset 1 (id:??) landed as
https://crrev.com/23a2e942e6bcd0797761ad0e2f0a2be4f32ce238
Cr-Commit-Position: refs/heads/master@{#345811}