Don't skip native "dispose" operation for children excluded from layout

When a composite is disposed no individual "dispose" operations are sent
to the native client for the children. This is because the native client
is already aware of the children and can dispose them directly.

However, in case "excludeFromLayout" is set to true the widget is no
longer attached to it's parent on the native side. This caused a
memory leak since these children effectively become orphans, marked
as disposed in JavaScript but still in memory on the native side.

Change-Id: Iaa2eead31251afdd0355a2007fb4b313ebcea805

Author: tbuschto

src/tabris/widgets/Composite.js

@@ -157,7 +157,8 @@ export default class Composite extends Widget {
     if (this.$children) {
       const children = this.$children.concat();
       for (let i = 0; i < children.length; i++) {
-        children[i]._dispose(true);
+        const skipNative = !children[i].excludeFromLayout;
+        children[i]._dispose(skipNative);
       }
       this.$children = undefined;
     }

test/tabris/widgets/Widget.test.js

@@ -474,12 +474,19 @@ describe('Widget', function() {
         expect(client.calls({op: 'destroy', id: parent.cid}).length).to.equal(1);
       });
 
-      it('does not DESTROY native children', function() {
+      it('does not DESTROY native children in layout', function() {
         parent.dispose();
 
         expect(client.calls({op: 'destroy', id: child.cid}).length).to.equal(0);
       });
 
+      it('does DESTROY native children excluded from layout', function() {
+        child.excludeFromLayout = true;
+        parent.dispose();
+
+        expect(client.calls({op: 'destroy', id: child.cid}).length).to.equal(1);
+      });
+
       it('notifies parent\'s `removeChild` listener', function() {
         const listener = spy();
         parent.onRemoveChild(listener);