Bug 917160 - AssureBlitted before switching EGLSurfaces with MakeCurrent. - r=bjacob

gfx/gl/GLContextProviderEGL.cpp

@@ -475,6 +475,15 @@ public:
             return;
 
         // Else, surface changed...
+        if (Screen()) {
+            /* Blit `draw` to `read` if we need to, before we potentially juggle
+             * `read` around. If we don't, we might attach a different `read`,
+             * and *then* hit AssureBlitted, which will blit a dirty `draw` onto
+             * the wrong `read`!
+             */
+            Screen()->AssureBlitted();
+        }
+
         mCurSurface = eglSurface;
         MakeCurrent(true);
     }