Made Ender Dragons fire EntityRegainHealth events when getting healed by Ender Crystals.

src/main/java/net/minecraft/server/EntityEnderDragon.java

@@ -9,8 +9,8 @@ import org.bukkit.craftbukkit.CraftWorld;
 import org.bukkit.event.entity.EntityDamageByEntityEvent;
 import org.bukkit.event.entity.EntityDamageEvent;
 import org.bukkit.event.entity.EntityExplodeEvent;
-import org.bukkit.Location;
 import org.bukkit.event.entity.EntityCreatePortalEvent;
+import org.bukkit.event.entity.EntityRegainHealthEvent;
 
 import java.util.ArrayList;
 import org.bukkit.PortalType;
@@ -346,7 +346,14 @@ public class EntityEnderDragon extends EntityComplex {
 
                 this.s = null;
             } else if (this.ticksLived % 10 == 0 && this.health < this.t) {
-                ++this.health;
+                // CraftBukkit start
+                EntityRegainHealthEvent event = new EntityRegainHealthEvent(this.getBukkitEntity(), 1, EntityRegainHealthEvent.RegainReason.ENDER_CRYSTAL);
+                this.world.getServer().getPluginManager().callEvent(event);
+
+                if (!event.isCancelled()) {
+                    this.health += event.getAmount();
+                }
+                // CraftBukkit end
             }
         }