Linux: fix build with system libevent.

Linux: fix build with system libevent.

message_pump_libevent_unittest.cc uses libevent directly, and it must get USE_SYSTEM_LIBEVENT symbol to work correctly with libevent. To make that work, base_unittests must depend on libevent.gyp, which uses direct_dependent_settings to set USE_SYSTEM_LIBEVENT.

This is upstreaming a Gentoo Linux patch.

BUG=none

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=95519

[Evan Martin, 2011-08-04 21:44:02]

Why is this needed?  I see a dep on libevent already in base.gypi

[Paweł Hajdan Jr., 2011-08-04 21:54:23]

On 2011/08/04 21:44:02, Evan Martin wrote:
> Why is this needed?  I see a dep on libevent already in base.gypi

But the dep does not apply to base_unittests, and we don't get the
USE_SYSTEM_LIBEVENT symbol, so the thing tries to use the bundled header. Gentoo
Linux removes bundled libs completely, and it detects breakages like this.

[Evan Martin, 2011-08-04 21:55:58]

On 2011/08/04 21:54:23, Paweł Hajdan Jr. wrote:
> On 2011/08/04 21:44:02, Evan Martin wrote:
> > Why is this needed?  I see a dep on libevent already in base.gypi
> 
> But the dep does not apply to base_unittests, and we don't get the
> USE_SYSTEM_LIBEVENT symbol, so the thing tries to use the bundled header.
Gentoo
> Linux removes bundled libs completely, and it detects breakages like this.

What tries to use the bundled header?

[Paweł Hajdan Jr., 2011-08-04 22:03:41]

On 2011/08/04 21:55:58, Evan Martin wrote:
> What tries to use the bundled header?

message_pump_libevent_unittest.cc ; if it's still not clear could you ping me on
IM? I'd be glad to explain what's going on here, but I'm pretty sure this is the
right fix.

[Evan Martin, 2011-08-04 22:17:57]

On 2011/08/04 22:03:41, Paweł Hajdan Jr. wrote:
> On 2011/08/04 21:55:58, Evan Martin wrote:
> > What tries to use the bundled header?
> 
> message_pump_libevent_unittest.cc ; if it's still not clear could you ping me
on
> IM? I'd be glad to explain what's going on here, but I'm pretty sure this is
the
> right fix.

Ah, that makes sense.  Can you make the review description mention this? 
(specifically that there's a unittest that calls into libevent direclty)

[Evan Martin, 2011-08-04 22:18:18]

(LGTM with that)