Barclays pointed out in a report on China energy demand back in October that improving industrial activities and new refining capacity in China are fueling the pick up in demand.
Now, China appears to be picking up this newly available market share, a mutually beneficial arrangement, as Iran needs the gasoline and China has surplus refining and shipping capacity.
But, even if China had heavy-crude refining capacity--which it doesn't--it wouldn't make economic sense to trade the four-day boat trip to Houston for a 40-day ride across the Pacific.