  We present the cosmological analysis of 752 photometrically-classified Type
Ia Supernovae (SNe Ia) obtained from the full Sloan Digital Sky Survey II
(SDSS-II) Supernova (SN) Survey, supplemented with host-galaxy spectroscopy
from the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). Our
photometric-classification method is based on the SN typing technique of Sako
et al. (2011), aided by host galaxy redshifts (0.05<z<0.55). SNANA simulations
of our methodology estimate that we have a SN Ia typing efficiency of 70.8%,
with only 3.9% contamination from core-collapse (non-Ia) SNe. We demonstrate
that this level of contamination has no effect on our cosmological constraints.
We quantify and correct for our selection effects (e.g., Malmquist bias) using
simulations. When fitting to a flat LambdaCDM cosmological model, we find that
our photometric sample alone gives omega_m=0.24+0.07-0.05 (statistical errors
only). If we relax the constraint on flatness, then our sample provides
competitive joint statistical constraints on omega_m and omega_lambda,
comparable to those derived from the spectroscopically-confirmed three-year
Supernova Legacy Survey (SNLS3). Using only our data, the statistics-only
result favors an accelerating universe at 99.96% confidence. Assuming a
constant wCDM cosmological model, and combining with H0, CMB and LRG data, we
obtain w=-0.96+0.10-0.10, omega_m=0.29+0.02-0.02 and omega_k=0.00+0.03-0.02
(statistical errors only), which is competitive with similar spectroscopically
confirmed SNe Ia analyses. Overall this comparison is re-assuring, considering
the lower redshift leverage of the SDSS-II SN sample (z<0.55) and the lack of
spectroscopic confirmation used herein. These results demonstrate the potential
of photometrically-classified SNe Ia samples in improving cosmological
constraints.
