function DiffChange(originalStart, originalLength, modifiedStart, modifiedLength) {
            //Debug.Assert(originalLength > 0 || modifiedLength > 0, "originalLength and modifiedLength cannot both be <= 0");
            this.originalStart = originalStart;
            this.originalLength = originalLength;
            this.modifiedStart = modifiedStart;
            this.modifiedLength = modifiedLength;
        }
Constructs a new DiffChange with the given sequence information
and content.