Fix component build for CrOS v4l2

Fix component build for CrOS v4l2

GetLastEGLErrorString must be exported since is now used from content
since r310941 ("Reland: V4L2VDA: Generalize EGLImage import and query
driver for output formats.").

BUG=none
TEST=build CrOS chrome for link

Committed: https://crrev.com/d248b4f1f5173f7c88af60f43fbfbfe0687fdd1d
Cr-Commit-Position: refs/heads/master@{#316650}

[spang, 2015-02-13 23:28:15]

spang@chromium.org changed reviewers:
+ sievers@chromium.org

[spang, 2015-02-13 23:28:57]

spang@chromium.org changed reviewers:
+ kbr@chromium.org
- sievers@chromium.org

[Ken Russell (switch to Gerrit), 2015-02-16 10:31:37]

lgtm

[spang, 2015-02-17 19:01:54]

The CQ bit was checked by spang@chromium.org

[commit-bot: I haz the power, 2015-02-17 19:03:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/924183002/1

[commit-bot: I haz the power, 2015-02-17 20:55:36]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-17 20:56:19]

Patchset 1 (id:??) landed as
https://crrev.com/d248b4f1f5173f7c88af60f43fbfbfe0687fdd1d
Cr-Commit-Position: refs/heads/master@{#316650}