gl_context_glx: add workaround to create default context

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 247535e3de5f065703d2cf3dd3ae8bfaa52f43bd..146c8d555dc981156ccc73382f144ce1a72b3546 100644
--- a/ui/gl/gl_switches.cc
+++ b/ui/gl/gl_switches.cc
@@ -25,6 +25,10 @@ const char kANGLEImplementationOpenGLESName[] = "gles";
 
 namespace switches {
 
+// Ask the GLX driver for the default context instead of trying to get the
+// highest version possible.
+const char kCreateDefaultGLContext[] = "create-default-gl-context";
+
 // Disables use of D3D11.
 const char kDisableD3D11[]                  = "disable-d3d11";