chromeos: forces kOverrideUseSoftwareGLForTests for ash_unittests

Without this tests that try to connect to ash a service hang. I get the
following gl errors:

libGL error: No matching fbConfigs or visuals found
libGL error: failed to load driver: swrast
[171208:171216:0802/122357.849400:5628725490183:ERROR:gl_context_glx.cc(227)] Couldn't make context current with X drawable.
[171208:171216:0802/122357.849448:5628725490229:ERROR:gpu_info_collector.cc(68)] gl::GLContext::MakeCurrent() failed

BUG=869739
TEST=test only change

Change-Id: Ib3fa4e01c715664e17bdcafd1af0ca98c34ff2dc
Reviewed-on: https://chromium-review.googlesource.com/1161171Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581250}

ash/test/ash_test_suite.cc

@@ -16,6 +16,7 @@
 #include "ui/base/ui_base_switches.h"
 #include "ui/compositor/test/context_factories_for_test.h"
 #include "ui/gfx/gfx_paths.h"
+#include "ui/gl/gl_switches.h"
 #include "ui/gl/test/gl_surface_test_support.h"
 
 namespace ash {
@@ -26,6 +27,12 @@ AshTestSuite::~AshTestSuite() = default;
 
 void AshTestSuite::Initialize() {
   base::TestSuite::Initialize();
+
+  // Force software-gl. This is necessary for tests that trigger launching ash
+  // in its own process
+  base::CommandLine* cmd_line = base::CommandLine::ForCurrentProcess();
+  cmd_line->AppendSwitch(switches::kOverrideUseSoftwareGLForTests);
+
   gl::GLSurfaceTestSupport::InitializeOneOff();
 
   gfx::RegisterPathProvider();