Add src/extensions to All target in gyp

Add src/extensions to All target in gyp

Use the same condition as chromium_builder_tests.

The targets are already in all_gn, and run on the trybots
via the chromium_builder_tests target. Putting them in All
just helps developers spot compile errors locally, before
they're caught by the bots.

Committed: https://crrev.com/f42e70932de69422378f3fef25df8afc4f2bb8e1
Cr-Commit-Position: refs/heads/master@{#324739}

[tapted, 2015-04-10 09:07:07]

tapted@chromium.org changed reviewers:
+ dpranke@chromium.org

[tapted, 2015-04-10 09:07:47]

Hi Dirk, please take a look

[Dirk Pranke, 2015-04-10 17:01:37]

lgtm

[tapted, 2015-04-11 01:03:45]

The CQ bit was checked by tapted@chromium.org

[commit-bot: I haz the power, 2015-04-11 01:04:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1053563004/1

[commit-bot: I haz the power, 2015-04-11 01:19:35]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-11 01:20:20]

Patchset 1 (id:??) landed as
https://crrev.com/f42e70932de69422378f3fef25df8afc4f2bb8e1
Cr-Commit-Position: refs/heads/master@{#324739}