Migrate Java code to separate QL repo.

java/ql/test/library-tests/dataflow/fields/B.java

@@ -0,0 +1,38 @@
+public class B {
+
+  public void f1() {
+    Elem e = new Elem();
+    Box1 b1 = new Box1(e, null);
+    Box2 b2 = new Box2(b1);
+    sink(b2.box1.elem1); // flow
+    sink(b2.box1.elem2); // FP due to flow in f2 below
+  }
+
+  public void f2() {
+    Elem e = new Elem();
+    Box1 b1 = new Box1(null, e);
+    Box2 b2 = new Box2(b1);
+    sink(b2.box1.elem1); // FP due to flow in f1 above
+    sink(b2.box1.elem2); // flow
+  }
+
+  public static void sink(Object o) { }
+
+  public static class Elem { }
+
+  public static class Box1 {
+    public Elem elem1;
+    public Elem elem2;
+    public Box1(Elem e1, Elem e2) {
+      this.elem1 = e1;
+      this.elem2 = e2;
+    }
+  }
+
+  public static class Box2 {
+    public Box1 box1;
+    public Box2(Box1 b1) {
+      this.box1 = b1;
+    }
+  }
+}