Allow tests to stub out GL draw calls.

ui/gl/gl_switches.cc

Index: ui/gl/gl_switches.cc
diff --git a/ui/gl/gl_switches.cc b/ui/gl/gl_switches.cc
index 5ac514878b431da28c0cec136ff60b5f1dbb8a64..b747d8f7ea9e5466a288eb224e68d5f367439de0 100644
--- a/ui/gl/gl_switches.cc
+++ b/ui/gl/gl_switches.cc
@@ -67,6 +67,10 @@ const char kGpuSwitchingOptionNameForceDiscrete[]   = "force_discrete";
 // library first, but fall back to regular library if loading fails.
 const char kTestGLLib[]                     = "test-gl-lib";
 
+// Disables GL drawing operations which produce pixel output. With this
+// the GL output will not be correct but tests will run faster.
+const char kDisableGLDrawingForTests[] = "disable-gl-drawing-for-tests";
+
 // This is the list of switches passed from this file that are passed from the
 // GpuProcessHost to the GPU Process. Add your switch to this list if you need
 // to read it in the GPU process, else don't add it.