Fix shim_headers.gypi to properly set up include paths

Fix shim_headers.gypi to properly set up include paths

when build/linux/unbundle is used.

Previously gyp files would contain a giant conditional sections depending on use_system_foo condition. After extracting that to build/linux/unbundle, the nesting depth got reduced by one level, so one less "+" in this .gypi file (otherwise the section does not get applied at all).

BUG=226860
R=rsleevi@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=197955

[Ryan Sleevi, 2013-05-02 19:08:56]

LGTM, but it would be helpful if your commit message / review description
explained more about the motivation for this change:

eg: Why it was wrong before, why it is right now

Since this is a very subtle aspect of GYP (that you can use + multiple times for
even more precedence)

[Paweł Hajdan Jr., 2013-05-02 19:32:04]

On 2013/05/02 19:08:56, Ryan Sleevi wrote:
> LGTM, but it would be helpful if your commit message / review description
> explained more about the motivation for this change:
> 
> eg: Why it was wrong before, why it is right now
> 
> Since this is a very subtle aspect of GYP (that you can use + multiple times
for
> even more precedence)

Good suggestion, done.

[Paweł Hajdan Jr., 2013-05-02 19:36:27]

Committed patchset #1 manually as r197955 (presubmit successful).