Revert of [build] Use -O2 on linux by default

Revert of [build] Use -O2 on linux by default (patchset #1 id:1 of https://codereview.chromium.org/1963693004/ )

Reason for revert:
Causes regressions.

Original issue's description:
> [build] Use -O2 on linux by default
>
> This switches O2 -> O3 to match chromium's configuration.
>
> This makes the difference between gn and gyp a bit smaller
> before switching.
>
> BUG=chromium:474921
> LOG=n
>
> Committed: https://crrev.com/a37ab71e343b8cc24df05868b941a49e0c271376
> Cr-Commit-Position: refs/heads/master@{#36124}

TBR=jochen@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:474921
Committed: https://crrev.com/413d9e2f4135219dd8ffa82d743ed9302dbc0ca0
Cr-Commit-Position: refs/heads/master@{#36135}

[Michael Achenbach, 2016-05-10 12:07:55]

Created Revert of [build] Use -O2 on linux by default

[commit-bot: I haz the power, 2016-05-10 12:08:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1958253004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1958253004/1

[commit-bot: I haz the power, 2016-05-10 12:08:19]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-05-10 12:09:59]

Description was changed from

==========
Revert of [build] Use -O2 on linux by default (patchset #1 id:1 of
https://codereview.chromium.org/1963693004/ )

Reason for revert:
Causes regressions.

Original issue's description:
> [build] Use -O2 on linux by default
> 
> This switches O2 -> O3 to match chromium's configuration.
> 
> This makes the difference between gn and gyp a bit smaller
> before switching.
> 
> BUG=chromium:474921
> LOG=n
> 
> Committed: https://crrev.com/a37ab71e343b8cc24df05868b941a49e0c271376
> Cr-Commit-Position: refs/heads/master@{#36124}

TBR=jochen@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:474921
==========

to

==========
Revert of [build] Use -O2 on linux by default (patchset #1 id:1 of
https://codereview.chromium.org/1963693004/ )

Reason for revert:
Causes regressions.

Original issue's description:
> [build] Use -O2 on linux by default
>
> This switches O2 -> O3 to match chromium's configuration.
>
> This makes the difference between gn and gyp a bit smaller
> before switching.
>
> BUG=chromium:474921
> LOG=n
>
> Committed: https://crrev.com/a37ab71e343b8cc24df05868b941a49e0c271376
> Cr-Commit-Position: refs/heads/master@{#36124}

TBR=jochen@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:474921

Committed: https://crrev.com/413d9e2f4135219dd8ffa82d743ed9302dbc0ca0
Cr-Commit-Position: refs/heads/master@{#36135}
==========

[commit-bot: I haz the power, 2016-05-10 12:10:00]

Patchset 1 (id:??) landed as
https://crrev.com/413d9e2f4135219dd8ffa82d743ed9302dbc0ca0
Cr-Commit-Position: refs/heads/master@{#36135}