<｜begin▁of▁sentence｜>### Instruction:
As a web content manager responsible for managing and updating the company's website, you are tasked with ensuring that the visual representation of a simple connected graph of 4 vertices is accurate and user-friendly for website visitors. The graph is represented as an igraph Graph object, and you have a custom drawing function called `draw_graph` that utilizes a class similar to `AbstractGraphDrawer`. Your goal is to ensure that the 'fr' (Fruchterman-Reingold) layout is properly utilized for drawing the graph to enhance its visual presentation on the website.
### Response:
from igraph import Graph, Layout

def draw_graph(graph, layout=None):
    # This is a mock function to emulate how ensure_layout might be used within a graph drawer class
    drawer = AbstractGraphDrawer(graph)
    layout = drawer.ensure_layout(layout=layout, graph=graph)
    # Proceed with drawing operations using the ensured layout...

# Example usage:
g = Graph([(0, 1), (1, 2), (2, 3)])
# Draw the graph using 'fr' layout
# We don't see the inner workings of ensure_layout but can expect it to handle the layout string
# The call below just illustrates a scenario where ensure_layout would be called internally.
draw_graph(g, 'fr')
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