isInFrame
Returns true if @context is in the process of drawing to its surface.
This is the case between calls to method@Gdk.DrawContext.begin_frame and method@Gdk.DrawContext.end_frame. In this situation, drawing commands may be effecting the contents of the @context's surface.
Return
true if the context is between method@Gdk.DrawContext.begin_frame and method@Gdk.DrawContext.end_frame calls.