code: function(rad) {
              var c = Math.cos(rad);
              var s = Math.sin(rad);
              var m11 = this.m[0] * c + this.m[2] * s;
              var m12 = this.m[1] * c + this.m[3] * s;
              var m21 = this.m[0] * -s + this.m[2] * c;
              var m22 = this.m[1] * -s + this.m[3] * c;
              this.m[0] = m11;
              this.m[1] = m12;
              this.m[2] = m21;
              this.m[3] = m22;
              return this;
          }
docs: Apply rotation
  @method
  @memberof Kinetic.Transform.prototype
  @param {Number} rad  Angle in radians
  @returns {Kinetic.Transform}