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In new-style notification, system notification has different style from
other notifications such as web notifications.

This CL fixes sync error notification:
* The context header shows the title "Sign In".
* The context header has an accent color.
* "Update sync passphrase" button is removed.
* New MD icon is used.

If chrome://flags#enable-message-center-new-style-notification is
disabled, this CL has no effect.

Before: http://screen/kTTXQujdxao
After: http://screen/WoRuaLE732T

TEST=manually tested on chell device
BUG=775381

Change-Id: I8c030131a5a9241223b6b02601fabe4035e9b866
Reviewed-on: https://chromium-review.googlesource.com/722545
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Reviewed-by: Pavel Yatsuk <pavely@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509689}