Implement most of VMStack and some of Zygote.

Change-Id: I07e18259a0452a2a9b077148f4f1ca67d3f63427
diff --git a/src/runtime.cc b/src/runtime.cc
index 68f42af..5dc057e 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -455,7 +455,7 @@
   REGISTER(register_dalvik_system_VMDebug);
   REGISTER(register_dalvik_system_VMRuntime);
   REGISTER(register_dalvik_system_VMStack);
-  //REGISTER(register_dalvik_system_Zygote);
+  REGISTER(register_dalvik_system_Zygote);
   REGISTER(register_java_lang_Class);
   REGISTER(register_java_lang_Object);
   REGISTER(register_java_lang_Runtime);