[Webkit] Memory Leak in GraphicContext

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[Memory Leak in GraphicContext]
The function in GraphicContextCairoWin.cpp below will allocate a memory block to cairo_t*
static cairo_t* createCairoContextWithHDC(HDC hdc, bool hasAlpha)

We have to release memory when platform destory in GraphicContextCairo.cpp

void GraphicsContext::platformDestroy()
{
RefPtr<cairo_t> cr = platformContext()->cr();
cr.~RefPtr();
    delete m_data;
}