Enable extra API checks, add a check for zapped global handles

src/api.h

Index: src/api.h
diff --git a/src/api.h b/src/api.h
index ac6b8342c54160dd3e13e181cd9d9911e071a9a6..8628b2a960a020b5c111caa90c3d8f2e595581ed 100644
--- a/src/api.h
+++ b/src/api.h
@@ -294,6 +294,9 @@ MAKE_TO_LOCAL(ToLocal, DeclaredAccessorDescriptor, DeclaredAccessorDescriptor)
   v8::internal::Handle<v8::internal::To> Utils::OpenHandle(                 \
     const v8::From* that, bool allow_empty_handle) {                        \
     EXTRA_CHECK(allow_empty_handle || that != NULL);                        \
+    EXTRA_CHECK(that == NULL ||                                             \
+        !(*reinterpret_cast<v8::internal::To**>(                            \
+            const_cast<v8::From*>(that)))->IsFailure());                    \
     return v8::internal::Handle<v8::internal::To>(                          \
         reinterpret_cast<v8::internal::To**>(const_cast<v8::From*>(that))); \
   }