Congress passed the Investment Company Act of 1940, 15 U.S.C. §§ 80a-1 et seq., to protect mutual fund investors. Section 36(b) of the Act imposes on investment advisers, who often create and manage mutual funds, “a fiduciary duty with respect to the receipt of compensation for services” from a mutual fund, and gives fund shareholders a private right of action for breach of that duty. Id. § 80a-35(b).