Make valgrind happier and stop us leaking so much we can can't run the tests on a device.

Change-Id: Id8f45dde788fd84c10b0b5807b2d12eae529ba5e
diff --git a/src/jni_internal.cc b/src/jni_internal.cc
index 1746cc3..89519c4 100644
--- a/src/jni_internal.cc
+++ b/src/jni_internal.cc
@@ -2580,6 +2580,9 @@
   functions = &gNativeInterface;
 }
 
+JNIEnvExt::~JNIEnvExt() {
+}
+
 // JNI Invocation interface.
 
 extern "C" jint JNI_CreateJavaVM(JavaVM** p_vm, void** p_env, void* vm_args) {