[WebGL]WebKit will crash when GraphicsContext3D::createForCurrentGLContext() return null

[await_me]

if GraphicsContext3D::createForCurrentGLContext() return 0 in TextureMapperGL's constructor,WebKit will crash
serval code and call stack is like follow:
WebCore::TextureMapperGLData::SharedGLData::currentSharedGLData(context) {GLContextDataMap::iterator it = glContextDataMap().find(context->platformGraphicsContext3D());}
WebCore::TextureMapperGLData::TextureMapperGLData(GraphicsContext3D* context) :context(context),sharedData(TextureMapperGLData::SharedGLData::currentSharedGLData(this->context)){}
WebCore::TextureMapperGL::TextureMapperGL() { m_context3D = GraphicsContext3D::createForCurrentGLContext();m_data = new TextureMapperGLData(m_context3D.get());}

when GraphicsContext3D::createForCurrentGLContext() return null, the parameters(m_context3D,context) will be null.
but currentSharedGLData had used context without null-check.
this will make webkit crash.

createForCurrentGLContext() method is as follow:
PassRefPtr<GraphicsContext3D> GraphicsContext3D::createForCurrentGLContext()
{
    RefPtr<GraphicsContext3D> context = adoptRef(new GraphicsContext3D(Attributes(), 0, GraphicsContext3D::RenderToCurrentGLContext));
    return context->m_private ? context.release() : 0;
}

when port has something wrong, context->m_private will be null.