Auto merge of #16903 - paulrouget:makeCurrentOnNew, r=emilio

make gl context current on browser initialization

As explained in servo/webrender#1233, it's necessary to make the current gl context current when the browser is initialized, otherwise the wrong gl context might be used if another window is created before the initialization.

/cc @glennw

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components/servo/lib.rs

@@ -126,6 +126,8 @@ impl<Window> Browser<Window> where Window: WindowMethods + 'static {
         // Global configuration options, parsed from the command line.
         let opts = opts::get();
 
+        // Make sure the gl context is made current.
+        window.prepare_for_composite(0, 0);
 
         // Get both endpoints of a special channel for communication between
         // the client window and the compositor. This channel is unique because