Include GLTestContext_command_buffer.cpp in G3 build.

This is now required to build our GPU testing tools.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2587
NOTREECHECKS=true

Change-Id: I219665fbe50e9bbea9abb88a6d63c34b76ca92e6
Reviewed-on: https://skia-review.googlesource.com/2587
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Ben Wagner <benjaminwagner@google.com>
diff --git a/public.bzl b/public.bzl
index 1a6021f..2e73b13 100644
--- a/public.bzl
+++ b/public.bzl
@@ -438,7 +438,6 @@
         "tests/SkSL*.cpp",  # Excluded along with Vulkan.
         "tests/SVGDeviceTest.cpp",
         "tools/gpu/gl/angle/*",
-        "tools/gpu/gl/command_buffer/*",
         "tools/gpu/gl/egl/*",
         "tools/gpu/gl/glx/*",
         "tools/gpu/gl/iOS/*",