Add eglplatform_shim_x11 target to ozone GN build.

Add eglplatform_shim_x11 target to ozone GN build.

This is needed for the GN build of Chromecast. The correspoinding GYP
target is a loadable_module, but since this target type is not yet
supported in GN (http://crbug.com/380327), a shared lib will be a
temporary substitute on Linux.

BUG= b/17615224

Committed: https://crrev.com/27fc61463aaeeacee10b8965b343afcdaf5065d4
Cr-Commit-Position: refs/heads/master@{#339359}

[slan, 2015-07-17 22:59:13]

slan@chromium.org changed reviewers:
+ alokp@chromium.org, brettw@chromium.org, esum@chromium.org, spang@chromium.org

[slan, 2015-07-17 22:59:14]

The Cast GN build requires this .so. Although the GYP target is a
loadable_module, a shared_library functions well in our case.

I have guarded the target with "is_linux" in accordance with comment #1 of
crbug.com/380327. PTAL.

[spang, 2015-07-17 23:13:57]

lgtm

[esum, 2015-07-17 23:16:53]

lgtm

[slan, 2015-07-17 23:18:33]

The CQ bit was checked by slan@chromium.org

[commit-bot: I haz the power, 2015-07-17 23:19:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1236883005/20001

[commit-bot: I haz the power, 2015-07-17 23:58:24]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-07-17 23:59:22]

Patchset 2 (id:??) landed as
https://crrev.com/27fc61463aaeeacee10b8965b343afcdaf5065d4
Cr-Commit-Position: refs/heads/master@{#339359}