function pumpInput() {
      ++self.outstandingReadCount_;
      chrome.usb.interruptTransfer(self.handle_, {
        direction: 'in',
        endpoint: endpointAddress,
        length: reportSize
      }, function(info) {
        --self.outstandingReadCount_;
        if (info.resultCode) {
          var e = new Error('Error during interrupt transfer: ' +
              info.resultCode);
          e.code = resultCode;
          self.inputPump_(null, e);
          return;
        }
        var data = new Uint8Array(info.data);
        if (self.inputPump_(data, undefined)) {
          pumpInput();
        }
      });
    }
Begins the input pump.
This will claim the interface and hopefully start receiving data.
@private