Reland of Convert enable_pre_sync_backup flag to new flags system.

Reland of Convert enable_pre_sync_backup flag to new flags system. (patchset #1 id:1 of https://codereview.chromium.org/1490713002/ )

Reason for revert:
Speculative revert did not help. Relanding.

Original issue's description:
> Revert of Convert enable_pre_sync_backup flag to new flags system. (patchset #2 id:20001 of https://codereview.chromium.org/1487873003/ )
>
> Reason for revert:
> Speculative revert, CrOS compile broken, more info on the bug.
> BUG=563927
>
> Original issue's description:
> > Convert enable_pre_sync_backup flag to new flags system.
> >
> > This flag's usage is very isolated so is a good candidate for the new system. There is now a generated header for the #define rather than a global define.
> >
> > Reland of http://crrev.com/1478623004#ps60001
> > TBR=zea@chromium.org
> >
> > Committed: https://crrev.com/db7f9756dc6e236589b90c76d6fa0f1244601e78
> > Cr-Commit-Position: refs/heads/master@{#362365}
>
> TBR=zea@chromium.org,brettw@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
>
> Committed: https://crrev.com/3c201fa28b53246177fed8d6b9454da4b0625df2
> Cr-Commit-Position: refs/heads/master@{#362368}

TBR=zea@chromium.org,brettw@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=563927
Committed: https://crrev.com/4bcbb121d634b0d087af5e35dcefface2b33aec2
Cr-Commit-Position: refs/heads/master@{#362369}

[vabr (Chromium), 2015-12-01 09:45:38]

Created Reland of Convert enable_pre_sync_backup flag to new flags system.

[vabr (Chromium), 2015-12-01 09:46:11]

The CQ bit was unchecked by vabr@chromium.org

[vabr (Chromium), 2015-12-01 09:46:14]

The CQ bit was checked by vabr@chromium.org

[commit-bot: I haz the power, 2015-12-01 09:46:18]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1490723002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1490723002/1

[commit-bot: I haz the power, 2015-12-01 09:47:54]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-12-01 09:49:01]

Description was changed from

==========
Reland of Convert enable_pre_sync_backup flag to new flags system. (patchset #1
id:1 of https://codereview.chromium.org/1490713002/ )

Reason for revert:
Speculative revert did not help. Relanding.

Original issue's description:
> Revert of Convert enable_pre_sync_backup flag to new flags system. (patchset
#2 id:20001 of https://codereview.chromium.org/1487873003/ )
> 
> Reason for revert:
> Speculative revert, CrOS compile broken, more info on the bug.
> BUG=563927
> 
> Original issue's description:
> > Convert enable_pre_sync_backup flag to new flags system.
> >
> > This flag's usage is very isolated so is a good candidate for the new
system. There is now a generated header for the #define rather than a global
define.
> >
> > Reland of http://crrev.com/1478623004#ps60001
> > TBR=zea@chromium.org
> >
> > Committed: https://crrev.com/db7f9756dc6e236589b90c76d6fa0f1244601e78
> > Cr-Commit-Position: refs/heads/master@{#362365}
> 
> TBR=zea@chromium.org,brettw@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> 
> Committed: https://crrev.com/3c201fa28b53246177fed8d6b9454da4b0625df2
> Cr-Commit-Position: refs/heads/master@{#362368}

TBR=zea@chromium.org,brettw@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=563927
==========

to

==========
Reland of Convert enable_pre_sync_backup flag to new flags system. (patchset #1
id:1 of https://codereview.chromium.org/1490713002/ )

Reason for revert:
Speculative revert did not help. Relanding.

Original issue's description:
> Revert of Convert enable_pre_sync_backup flag to new flags system. (patchset
#2 id:20001 of https://codereview.chromium.org/1487873003/ )
>
> Reason for revert:
> Speculative revert, CrOS compile broken, more info on the bug.
> BUG=563927
>
> Original issue's description:
> > Convert enable_pre_sync_backup flag to new flags system.
> >
> > This flag's usage is very isolated so is a good candidate for the new
system. There is now a generated header for the #define rather than a global
define.
> >
> > Reland of http://crrev.com/1478623004#ps60001
> > TBR=zea@chromium.org
> >
> > Committed: https://crrev.com/db7f9756dc6e236589b90c76d6fa0f1244601e78
> > Cr-Commit-Position: refs/heads/master@{#362365}
>
> TBR=zea@chromium.org,brettw@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
>
> Committed: https://crrev.com/3c201fa28b53246177fed8d6b9454da4b0625df2
> Cr-Commit-Position: refs/heads/master@{#362368}

TBR=zea@chromium.org,brettw@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=563927

Committed: https://crrev.com/4bcbb121d634b0d087af5e35dcefface2b33aec2
Cr-Commit-Position: refs/heads/master@{#362369}
==========

[commit-bot: I haz the power, 2015-12-01 09:49:02]

Patchset 1 (id:??) landed as
https://crrev.com/4bcbb121d634b0d087af5e35dcefface2b33aec2
Cr-Commit-Position: refs/heads/master@{#362369}