Add -Xcheck:jni.

I think this is as complete as possible right now. The remaining
two #if 0 sections require:

1. a way to get the Method* of the current native method.
2. a way to get the Class* of the type of a given Field*.

Change-Id: I331586022095fb36ccc10c9ac1890a59a9224d01
diff --git a/test/MyClassNatives/MyClassNatives.java b/test/MyClassNatives/MyClassNatives.java
index 5203e4a..f462363 100644
--- a/test/MyClassNatives/MyClassNatives.java
+++ b/test/MyClassNatives/MyClassNatives.java
@@ -1,6 +1,7 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 
 class MyClass {
+    native void throwException();
     native void foo();
     native int fooI(int x);
     native int fooII(int x, int y);