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 7cd676e40f9e4dcd3773fa458a7044dec85decc4..85cca9e379ec14b40557e37f857269d26ad84c12 100644
--- a/ui/gl/gl_switches.cc
+++ b/ui/gl/gl_switches.cc
@@ -26,6 +26,10 @@ const char kANGLEImplementationNullName[]     = "null";
 
 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";