Fire ChunkWatchEvent.Watch event, closes #2767. Based on @sfPlayer1 patch suggestion. It looks like this logic has shifted relative to 1.8, so there may be differences in event behaviour now.

patches/minecraft/net/minecraft/server/management/PlayerChunkMapEntry.java.patch

@@ -23,7 +23,16 @@
      }
  
      public ChunkPos func_187264_a()
-@@ -71,6 +80,20 @@
+@@ -63,6 +72,8 @@
+             if (this.field_187290_j)
+             {
+                 this.func_187278_c(p_187276_1_);
++                // chunk watch event - the chunk is ready
++                net.minecraftforge.common.MinecraftForge.EVENT_BUS.post(new net.minecraftforge.event.world.ChunkWatchEvent.Watch(this.field_187284_d, p_187276_1_));
+             }
+         }
+     }
+@@ -71,6 +82,20 @@
      {
          if (this.field_187283_c.contains(p_187277_1_))
          {
@@ -44,7 +53,7 @@
              if (this.field_187290_j)
              {
                  p_187277_1_.field_71135_a.func_147359_a(new SPacketUnloadChunk(this.field_187284_d.field_77276_a, this.field_187284_d.field_77275_b));
-@@ -78,6 +101,8 @@
+@@ -78,6 +103,8 @@
  
              this.field_187283_c.remove(p_187277_1_);
  
@@ -53,7 +62,7 @@
              if (this.field_187283_c.isEmpty())
              {
                  this.field_187282_b.func_187305_b(this);
-@@ -87,6 +112,7 @@
+@@ -87,6 +114,7 @@
  
      public boolean func_187268_a(boolean p_187268_1_)
      {
@@ -61,7 +70,16 @@
          if (this.field_187286_f != null)
          {
              return true;
-@@ -167,7 +193,7 @@
+@@ -131,6 +159,8 @@
+             {
+                 entityplayermp.field_71135_a.func_147359_a(spacketchunkdata);
+                 this.field_187282_b.func_72688_a().func_73039_n().func_85172_a(entityplayermp, this.field_187286_f);
++                // chunk watch event - delayed to here as the chunk wasn't ready in addPlayer
++                net.minecraftforge.common.MinecraftForge.EVENT_BUS.post(new net.minecraftforge.event.world.ChunkWatchEvent.Watch(this.field_187284_d, entityplayermp));
+             }
+ 
+             return true;
+@@ -167,7 +197,7 @@
  
              this.field_187288_h |= 1 << (p_187265_2_ >> 4);
  
@@ -70,7 +88,7 @@
              {
                  short short1 = (short)(p_187265_1_ << 12 | p_187265_3_ << 8 | p_187265_2_);
  
-@@ -178,7 +204,8 @@
+@@ -178,7 +208,8 @@
                          return;
                      }
                  }
@@ -80,7 +98,7 @@
                  this.field_187285_e[this.field_187287_g++] = short1;
              }
          }
-@@ -195,6 +222,7 @@
+@@ -195,6 +226,7 @@
          }
      }
  
@@ -88,7 +106,7 @@
      public void func_187280_d()
      {
          if (this.field_187290_j && this.field_187286_f != null)
-@@ -208,28 +236,32 @@
+@@ -208,28 +240,32 @@
                      int k = (this.field_187285_e[0] >> 8 & 15) + this.field_187284_d.field_77275_b * 16;
                      BlockPos blockpos = new BlockPos(i, j, k);
                      this.func_187267_a(new SPacketBlockChange(this.field_187282_b.func_72688_a(), blockpos));

src/main/java/net/minecraftforge/event/world/ChunkWatchEvent.java

@@ -41,7 +41,7 @@ public class ChunkWatchEvent extends Event
     /**
      * ChunkWatchEvent.Watch is fired when an EntityPlayer begins watching a chunk.<br>
      * This event is fired when a chunk is added to the watched chunks of an EntityPlayer in
-     * {@link EntityPlayerMP#onUpdate()}. <br>
+     * {@link PlayerChunkMapEntry#addPlayer(EntityPlayerMP)} and {@link PlayerChunkMapEntry#sentToPlayers()}. <br>
      * <br>
      * This event is not {@link Cancelable}.<br>
      * <br>