Bug 501428. SMIL: Optimize nsSMILKeySpline::CalcBezier. r=dholbert, r=longsonr

Eliminates the call to pow() and reduces the number of multiplications from 4
to 3.

content/smil/nsSMILKeySpline.cpp

@@ -78,7 +78,8 @@ nsSMILKeySpline::CalcBezier(double aT,
                             double aA1,
                             double aA2)
 {
-  return A(aA1, aA2) * pow(aT,3) + B(aA1, aA2)*aT*aT + C(aA1) * aT;
+  // use Horner's scheme to evaluate the Bezier polynomial
+  return ((A(aA1, aA2)*aT + B(aA1, aA2))*aT + C(aA1))*aT;
 }
 
 /*static*/ double