Update specmap and sb2 import to add new fields to layering blocks.

src/serialization/sb2.js

@@ -601,6 +601,20 @@ const parseBlock = function (sb2block, addBroadcastMsg, getVariableId, extension
             }
         }
     }
+
+    // Updated layering blocks
+    if (oldOpcode === 'comeToFront') {
+        activeBlock.fields.FRONT_BACK = {
+            name: 'FRONT_BACK',
+            value: 'front'
+        };
+    } else if (oldOpcode === 'goBackByLayers:') {
+        activeBlock.fields.FORWARD_BACKWARD = {
+            name: 'FORWARD_BACKWARD',
+            value: 'backward'
+        };
+    }
+
     // Special cases to generate mutations.
     if (oldOpcode === 'stopScripts') {
         // Mutation for stop block: if the argument is 'other scripts',

src/serialization/sb2_specmap.js

@@ -345,12 +345,12 @@ const specMap = {
         ]
     },
     'comeToFront': {
-        opcode: 'looks_gotofront',
+        opcode: 'looks_gotofrontback',
         argMap: [
         ]
     },
     'goBackByLayers:': {
-        opcode: 'looks_gobacklayers',
+        opcode: 'looks_goforwardbackwardlayers',
         argMap: [
             {
                 type: 'input',

test/unit/sprites_rendered-target.js

@@ -293,8 +293,12 @@ test('layers', t => {
     a.renderer = renderer;
     a.goToFront();
     t.equals(a.renderer.order, 5);
-    a.goBackLayers(2);
+    a.goBackwardLayers(2);
     t.equals(a.renderer.order, 3);
+    a.goToBack();
+    t.equals(a.renderer.order, 1);
+    a.goForwardLayers(1);
+    t.equals(a.renderer.order, 2);
     o.drawableID = 999;
     a.goBehindOther(o);
     t.equals(a.renderer.order, 1);