Use 16 instead of 4 for determining member offsets.

src/base/macros.h

Index: src/base/macros.h
diff --git a/src/base/macros.h b/src/base/macros.h
index 80a89496a5e25bc06caf3aa6445cdbb11b484303..371d7da6eaa72251a9693096f64a79def1b8fa49 100644
--- a/src/base/macros.h
+++ b/src/base/macros.h
@@ -20,9 +20,9 @@
 // corresponds to 'offsetof' (in stddef.h), except that it doesn't
 // use 0 or NULL, which causes a problem with the compiler warnings
 // we have enabled (which is also why 'offsetof' doesn't seem to work).
-// Here we simply use the non-zero value 4, which seems to work.
-#define OFFSET_OF(type, field)                                          \
-  (reinterpret_cast<intptr_t>(&(reinterpret_cast<type*>(4)->field)) - 4)
+// Here we simply use the aligned, non-zero value 16.
+#define OFFSET_OF(type, field) \
+  (reinterpret_cast<intptr_t>(&(reinterpret_cast<type*>(16)->field)) - 16)
 
 
 #if V8_OS_NACL