Use HyperlinkPreference where applicable.

Use HyperlinkPreference where applicable.

Settings contains several "learn more" links that are actually
preference objects. These were originally implemented as
TextMessagePreferences with some ad-hoc logic to change the text
formatting and click handling. Now we have a dedicated
HyperlinkPreference class to encapsulate this logic, so use it.

Committed: https://crrev.com/a135cb4208f3543ab144ff7f3f25df3a09dd5bb7
Cr-Commit-Position: refs/heads/master@{#316715}

[newt (away), 2015-02-18 00:03:37]

newt@chromium.org changed reviewers:
+ aurimas@chromium.org

[newt (away), 2015-02-18 00:03:38]

PTAL

[aurimas (slooooooooow), 2015-02-18 00:07:18]

lgtm

[newt (away), 2015-02-18 00:28:50]

The CQ bit was checked by newt@chromium.org

[commit-bot: I haz the power, 2015-02-18 00:29:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/933063002/1

[commit-bot: I haz the power, 2015-02-18 00:55:43]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-18 00:56:16]

Patchset 1 (id:??) landed as
https://crrev.com/a135cb4208f3543ab144ff7f3f25df3a09dd5bb7
Cr-Commit-Position: refs/heads/master@{#316715}