Introduce --zap-cpp-pointers (off by default)

src/factory.cc

Index: src/factory.cc
diff --git a/src/factory.cc b/src/factory.cc
index 22f2e639106df8d3c3a4ed54f0b166553256bd58..eef3e197b6ea1e706825eac2597880a712d74dfb 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -34,8 +34,22 @@ namespace internal {
     return Handle<TYPE>(TYPE::cast(__object__), ISOLATE); \
   }
 
+// TODO(jkummerow): Handlify more of heap.cc to maintain the rule that
+// "there are no raw pointers anywhere on the stack when an allocation
+// is happening", and then move the ZapHeapPointersInCppFrames() call
+// into Heap::AllocateRaw.
+#if DEBUG
+#define MAYBE_ZAP_STACK(isolate)         \
+  if (FLAG_zap_cpp_pointers) {           \
+    ZapHeapPointersInCppFrames(isolate); \
+  }
+#else
+#define MAYBE_ZAP_STACK(isolate)
+#endif
+
 #define CALL_HEAP_FUNCTION(ISOLATE, FUNCTION_CALL, TYPE)                      \
   do {                                                                        \
+    MAYBE_ZAP_STACK(ISOLATE);                                                 \
     AllocationResult __allocation__ = FUNCTION_CALL;                          \
     Object* __object__ = NULL;                                                \
     RETURN_OBJECT_UNLESS_RETRY(ISOLATE, TYPE)                                 \