Fix MB configs for public PGO builders.

Fix MB configs for public PGO builders.

The public PGO builders do not do chrome-branded builds, so
can't reuse the existing 'official' mixin and need to split out
is_official_build from is_chrome_branded.

TBR=sebmarchand@chromium.org
NOTRY=true
BUG=595947
Committed: https://crrev.com/9ef9d8e872aaac97e62099495d5d1c8d9a61d8f3
Cr-Commit-Position: refs/heads/master@{#407230}

[Dirk Pranke, 2016-07-22 19:18:52]

skipping the trybots since we don't have any trybots that would be affected by
this.

[Dirk Pranke, 2016-07-22 19:18:56]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2016-07-22 19:19:41]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-07-22 19:25:18]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-07-22 19:26:55]

Description was changed from

==========
Fix MB configs for public PGO builders.

The public PGO builders do not do chrome-branded builds, so
can't reuse the existing 'official' mixin and need to split out
is_official_build from is_chrome_branded.

TBR=sebmarchand@chromium.org
NOTRY=true
BUG=595947
==========

to

==========
Fix MB configs for public PGO builders.

The public PGO builders do not do chrome-branded builds, so
can't reuse the existing 'official' mixin and need to split out
is_official_build from is_chrome_branded.

TBR=sebmarchand@chromium.org
NOTRY=true
BUG=595947

Committed: https://crrev.com/9ef9d8e872aaac97e62099495d5d1c8d9a61d8f3
Cr-Commit-Position: refs/heads/master@{#407230}
==========

[commit-bot: I haz the power, 2016-07-22 19:26:56]

Patchset 1 (id:??) landed as
https://crrev.com/9ef9d8e872aaac97e62099495d5d1c8d9a61d8f3
Cr-Commit-Position: refs/heads/master@{#407230}