#2745 Set vflex to cell in Vbox cause js error

[jimmy shiau]

<vbox width="100px" height="100px" align="stretch">
<cell vflex="1">
<div style="background: blue" vflex="1"/>
</cell>
<cell vflex="1">
<div style="background: yellow" vflex="1"/>
</cell>
</vbox>

[jimmy shiau]

Fixed since June 28 2011