Port gfx_jni_headers target to GN build.

Port gfx_jni_headers target to GN build.

In Debug build:

$ gn gen out/Debug --args='os="android" cpu_arch="x86"'

$ ninja -C out/Debug gfx_jni_headers

In Release build:

$ gn gen out/Debug --args='is_debug=false os="android" cpu_arch="x86"'

$ ninja -C out/Release gfx_jni_headers

BUG=None
TEST=see above
R=cjhopman@chromium.org
TBR=ben@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=270319

[tfarina, 2014-05-13 19:26:20]

Trying with Scott.

Moving Brett to CC list.

Scott, do you mind reviewing this to me instead?

Thanks,

[scottmg, 2014-05-13 19:29:54]

->Chris

[cjhopman, 2014-05-13 19:50:30]

lgtm

[tfarina, 2014-05-14 03:18:42]

Committed patchset #1 manually as r270319 (presubmit successful).