Deletion barrier: Distinguish+verify field initialization in ia32 generated code.

runtime/vm/heap.h

Index: runtime/vm/heap.h
===================================================================
--- runtime/vm/heap.h	(revision 42599)
+++ runtime/vm/heap.h	(working copy)
@@ -63,6 +63,13 @@
   static const intptr_t kHeapSizeInMB = kHeapSizeInMWords * kWordSize;
   static const intptr_t kCodeHeapSizeInMB = 18;
 
+#if defined(DEBUG)
+  // Pattern for unused new space and swept old space.
+  static const uint64_t kZap64Bits = 0xf3f3f3f3f3f3f3f3;
+  static const uint32_t kZap32Bits = static_cast<uint32_t>(kZap64Bits);
+  static const uint8_t kZapByte = static_cast<uint8_t>(kZap64Bits);
+#endif  // DEBUG
+
   ~Heap();
 
   Scavenger* new_space() const { return new_space_; }