Avoid group label text with lines

Layout.js

@@ -13,6 +13,7 @@ class Layout {
     this.resolveAffinity();
     this.resolveGroups();
     while (this.iterate());
+    this.addGroupPos();
     this.drawLinks();
     this.fixOrigin();
   }
@@ -194,6 +195,20 @@ class Layout {
     ];
   }
 
+  addGroupPos() {
+    for (let group of this.groups_) {
+      if (!group.hasGraphGroup()) {
+        continue;
+      }
+      let [min, max] = group.getMinMax();
+      for (let x = min[0]; x <= max[0]; ++x) {
+        for (let y = min[1]; y <= max[1]; ++y) {
+          getOrSet(this.nodesByPos_, [x, y], group);
+        }
+      }
+    }
+  }
+
   drawLinks() {
     let links = [];
     for (let from of this.nodes_) {

LayoutGroup.js

@@ -81,4 +81,8 @@ class LayoutGroup {
       label: this.graphGroup_.label,
     };
   }
+
+  hasGraphGroup() {
+    return this.graphGroup_ != null;
+  }
 }