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

src/frames.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_FRAMES_H_
 #define V8_FRAMES_H_
 
 #include "src/allocation.h"
 #include "src/flags.h"
 #include "src/handles.h"
@@ skipping 1588 matching lines @@
 
  private:
   StackFrameIterator iterator_;
 };
 
 
 // Reads all frames on the current stack and copies them into the current
 // zone memory.
 Vector<StackFrame*> CreateStackMap(Isolate* isolate, Zone* zone);
 
+#ifdef DEBUG
+// Walks the stack, finds sections belonging to C++ frames, looks for values
+// that look like heap pointers inside them, and zaps them. Intended to flush
+// out GC safety issues; only call this when the program must be prepared for
+// GC to happen.
+void ZapHeapPointersInCppFrames(Isolate* isolate, ThreadLocalTop* t = NULL);
+#endif
+
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_FRAMES_H_