The ornamental design for a vehicle chassis, as shown and described.
FIG. 1 is a top plan view of a vehicle chassis showing my new design, as shown in one environment being in broken lines, the environment not being a part of the disclosed and claimed design;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a right side elevational view thereof;
FIG. 4 is a left side elevational view thereof; and,