Hold a ClassLoader reference in NativeAllocationRegistry.

So that the native library isn't unloaded before we have a chance to
call the freeFunction.

Bug: 28406866

(cherry picked from commit 7d3c7390a8cbeff12fe790e5d12da6e07cf8c298)

Change-Id: I38edb9ba6855ef98743001e4bbf4fd80fb27873d
diff --git a/tools/ahat/test-dump/Main.java b/tools/ahat/test-dump/Main.java
index d61a98d..3936f29 100644
--- a/tools/ahat/test-dump/Main.java
+++ b/tools/ahat/test-dump/Main.java
@@ -50,7 +50,8 @@
         bigArray[i] = (byte)((i*i) & 0xFF);
       }
 
-      NativeAllocationRegistry registry = new NativeAllocationRegistry(0x12345, 42);
+      NativeAllocationRegistry registry = new NativeAllocationRegistry(
+          Main.class.getClassLoader(), 0x12345, 42);
       registry.registerNativeAllocation(anObject, 0xABCDABCD);
     }
   }