Do not iterate past the end on processing leaf class.

tools/clang/blink_gc_plugin/tests/left_most_gc_base.h

Index: tools/clang/blink_gc_plugin/tests/left_most_gc_base.h
diff --git a/tools/clang/blink_gc_plugin/tests/left_most_gc_base.h b/tools/clang/blink_gc_plugin/tests/left_most_gc_base.h
index f9bc6dd13b69b8dc6b8636c7b240a624f7729795..0d76d6161f4046e0651f0fbda3d72f447c08f279 100644
--- a/tools/clang/blink_gc_plugin/tests/left_most_gc_base.h
+++ b/tools/clang/blink_gc_plugin/tests/left_most_gc_base.h
@@ -18,6 +18,13 @@ class Left : public GarbageCollected<Left>, public B, public A { };
 class DerivedRight : public Right, public Left { };  // Error
 class DerivedLeft : public Left, public Right { };
 
+class C : public GarbageCollected<C> {
+public:
+    virtual void trace(Visitor*);
+};
+
+class IllFormed : public A, public C { }; // Error
+
 }
 
 #endif