gpu/khronos_glcts_support: Move target_defaults into separate file

gpu/khronos_glcts_support: Move target_defaults into separate file

Move the target_defaults into its own gypi file so that we can
parse the variables in khronos_glcts.gypi with the gypi_to_gn.py
script.  The gypi_to_gn.py chokes on target_defaults.

BUG=chromium:412865, chromium:471903
R=kbr@chromium.org, piman@chromium.org, dpranke@chromium.org
TEST=Verify khronos_glcts_test builds and runs

Signed-off-by: U. Artie Eoff <ullysses.a.eoff@intel.com>;

Committed: https://crrev.com/f1f30573fd0060132feee853ec26e744ed09fe11
Cr-Commit-Position: refs/heads/master@{#356711}

[Dirk Pranke, 2015-10-28 23:47:57]

I defer this one to kbr or piman.

[piman, 2015-10-29 00:10:14]

lgtm

[U. Artie Eoff, 2015-10-29 00:29:03]

The CQ bit was checked by ullysses.a.eoff@intel.com

[commit-bot: I haz the power, 2015-10-29 00:29:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1427433007/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1427433007/20001

[Ken Russell (switch to Gerrit), 2015-10-29 00:37:14]

LGTM too. Thanks.

[commit-bot: I haz the power, 2015-10-29 00:55:25]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-29 00:56:58]

Patchset 2 (id:??) landed as
https://crrev.com/f1f30573fd0060132feee853ec26e744ed09fe11
Cr-Commit-Position: refs/heads/master@{#356711}