How does USB 3.0 negotiate power states?
I know that USB 2.0 negotiated power by tying the D+ and D- lines to specific voltages


Not as per USB Specification. The battery specification signals the "charger" via a short (low resitance) between D+ and D-.


  find any information on USB 3.0 power state negotiation


As in the USB 2.0 spec, look in the Standard Configuration Descriptor. The bMaxPower field definition is updated in the 3.0/3.1 USB specs. From USB_3_1_r1.0.pdf, Table 9-21:


  Expressed in 2-mA units when the
  device is operating in high-speed mode and in 8-mA
  units when operating at Gen X speed.