According to the special relativity, as measured from Earth, time in photon's frame is frozen. So, the 499 seconds must be in photon's frame.
If we measured in a frame where time were frozen, then the measured elapsed time would be 0 s, not 499 s.
So we cannot be talking about the photon's frame (which, as has been pointed out in comments and in answers to previous questions, doesn't exist).
We can't even be measuring in some frame that follows the path of the photon, taking the limit as its velocity relative to Earth approaches c. Because, again, in that case we'd measure an elapsed time close to 0, and not 499 s.
Further, the statement that "photon does not experience time" is valid only when the photon is viewed from a stationary frame of reference,
Every frame of reference is stationary when measured in its own frame. There is no way to distinguish a "stationary" frame from a "non-stationary" frame (except with reference to some other frame).
If the one-way speed of light has not been measured yet, then how can one assert that light takes 499 seconds to travel from the Sun to the earth?
We don't really measure the time it takes for light to travel from the Sun to the Earth, since we can't send an experimenter to the Sun to shine a laser at us. We measure the distance from the Sun to the Earth, and divide by the speed of light.
We are assuming the speed of light is the same in all directions, but in any case sometimes the Earth is on one side of the sun and sometimes it is on the other, so even if the speed of light weren't the same in different directions, ultimately the time for the light to travel from the Sun to Earth would average out to pretty close to the same 499 s.
