Call Blockly.svgResize() once the div it is going to be placed in (#489)

knows what size it is going to be.

demos/resizable/overlay.html

@@ -87,6 +87,7 @@
     };
     window.addEventListener('resize', onresize, false);
     onresize();
+    Blockly.svgResize(workspace);
   </script>
 </body>
 </html>