Revert "Revert "Keep internal stack trace methods declaring classes live""

Fixed some code which used old stack trace representation in throwable.cc.

Bug: 22720414

This reverts commit 45a8522898702f6a725ae19d97bceedc8fc609a6.

Change-Id: I7385075caf649ce76da5d8866fd0031b9e8e5ef4
diff --git a/test/141-class-unload/src/Main.java b/test/141-class-unload/src/Main.java
index 105a2b9..3cc43ac 100644
--- a/test/141-class-unload/src/Main.java
+++ b/test/141-class-unload/src/Main.java
@@ -39,6 +39,8 @@
             testNoUnloadInstance(constructor);
             // Test JNI_OnLoad and JNI_OnUnload.
             testLoadAndUnloadLibrary(constructor);
+            // Test that stack traces keep the classes live.
+            testStackTrace(constructor);
             // Stress test to make sure we dont leak memory.
             stressTest(constructor);
         } catch (Exception e) {
@@ -75,6 +77,16 @@
       System.out.println(loader.get());
     }
 
+    private static void testStackTrace(Constructor constructor) throws Exception {
+        WeakReference<Class> klass = setUpUnloadClass(constructor);
+        Method stackTraceMethod = klass.get().getDeclaredMethod("generateStackTrace");
+        Throwable throwable = (Throwable) stackTraceMethod.invoke(klass.get());
+        stackTraceMethod = null;
+        Runtime.getRuntime().gc();
+        boolean isNull = klass.get() == null;
+        System.out.println("class null " + isNull + " " + throwable.getMessage());
+    }
+
     private static void testLoadAndUnloadLibrary(Constructor constructor) throws Exception {
         WeakReference<ClassLoader> loader = setUpLoadLibrary(constructor);
         // No strong refernces to class loader, should get unloaded.