More info:
When I create a new world with the same seed the Dragon is alive as expected, and the pre-generated portal is there, too. So a workaround for everyone who has the same problem is this one:
1. Figure out your seed (e.g. using MCEdit)
2. Generate a new world with the same seed, preferably in Creative Mode (so you don't have to farm Eyes of Ender to activate the portal)
3. Go to The End, and go close enough to the obsidian pillar circle to make sure it's all generated
4. Leave the game
5. Copy the DIM1 folder from the cheat world to your original world
6. Enjoy your Drake!
@stephanie Dumas: As your player data is not stored in the DIM1 folder, you should be in the same place, with the same inventory, just with the dragon around when you try this. But please backup your world before you try, just to be sure.
I had already played my world in previous 1.9 snapshots, so it's possible that one of the previous snapshots has caused the problem. Or it may occur in 1.8 worlds generally, I can't tell. I also can't remember in which snapshots I actually entered The End.
This issue still exists in 15w32a. There is neither an Ender Dragon nor the pre-generated portal when I enter the End. My world is from 1.8, but I reset the End by deleting the DIM1 folder. I had not defeated the Dragon in 1.8.x in this world.
Forced crash report attached. My world's seed is -7136671779322761081 in case it matters.
Forced crash report in 15w32a in a world where the dragon doesn't spawn
I think this bug explains my experience too: I made a map in my town, "zoomed in" twice using shears and got a completely empty map, obviously not showing the location where I was.
To be honest, I think the new recipe with the shears is a bad idea anyway. Even when this bug is fixed and it somehow becomes possible to create 1:1 maps of every area, it's still very counter-intuitive to have different recipes for zooming in and out, uselessly more complicated than the old recipe, and will require using the F3 screen and calculating to figure out where you have to stand, then use the map, then cut it with shears, and THEN finally see if it's the location you wanted.
My personal preference is clearly a revert to the old recipe.