GN: Don't link source sets into static libraries

GN: Don't link source sets into static libraries

Previously if a static library depended on a source set, we'd link it in. This can easily cause multiple inclusions of the source set's code if there are multiple shared libraries that depend on it.

This patch forwards the source set up the dependency chain to the next linkable target (shared library or executable). This solves the multiple-definition problem. The downside is that if you make a static library that depends on a source set, it won't be "complete" in the sense that you can give it to somebody and it will have all of the files in it. If we need that capability, we'll add some kind of "complete" flag.

BUG=
R=scottmg@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=274024

[scottmg, 2014-05-31 02:55:08]

lgtm

[brettw, 2014-05-31 04:08:47]

The CQ bit was checked by brettw@chromium.org

[commit-bot: I haz the power, 2014-05-31 04:12:18]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/brettw@chromium.org/302033004/1

[brettw, 2014-05-31 04:41:54]

The CQ bit was unchecked by brettw@chromium.org

[brettw, 2014-05-31 04:41:58]

Committed patchset #1 manually as r274024 (presubmit successful).