ahat: show sample path through strong references.

Instead of showing a sample path through weak references, which is
much less useful for debugging why the object is retained.

Change-Id: I2b8d8bc9368cdcabd7a369e45278ba9b44a38e40
Bug: 64592321
Test: m ahat-test, with new gcRootPathNotWeak test added.
diff --git a/tools/ahat/test/InstanceTest.java b/tools/ahat/test/InstanceTest.java
index f0e7f44..e05782c 100644
--- a/tools/ahat/test/InstanceTest.java
+++ b/tools/ahat/test/InstanceTest.java
@@ -285,6 +285,18 @@
   }
 
   @Test
+  public void gcRootPathNotWeak() throws IOException {
+    TestDump dump = TestDump.getTestDump();
+
+    AhatInstance strong = dump.getDumpedAhatInstance("aLongStrongPathToSamplePathObject");
+    AhatInstance strong2 = strong.getField("referent").asAhatInstance();
+    AhatInstance object = strong2.getField("referent").asAhatInstance();
+
+    List<PathElement> path = object.getPathFromGcRoot();
+    assertEquals(strong2, path.get(path.size() - 2).instance);
+  }
+
+  @Test
   public void retainedSize() throws IOException {
     TestDump dump = TestDump.getTestDump();