a95435b836
IFrameCallback has a pure virtual method, but its destructor was non-virtual. While CanvasContext, which inherits from IFrameCallback, declares its own destructor virtual, this is not sufficient when accessing via an IFrameCallback pointer. We fix this by making the base destructor virtual. Test: Treehugger Change-Id: I6424f90c16caea417b5f80b60d76a7ca7c7ef97c