Fix deserializer to understand direct pointers from code to cell payloads.

src/x64/assembler-x64-inl.h

Index: src/x64/assembler-x64-inl.h
===================================================================
--- src/x64/assembler-x64-inl.h	(revision 12224)
+++ src/x64/assembler-x64-inl.h	(working copy)
@@ -309,10 +309,7 @@
 
 JSGlobalPropertyCell* RelocInfo::target_cell() {
   ASSERT(rmode_ == RelocInfo::GLOBAL_PROPERTY_CELL);
-  Address address = Memory::Address_at(pc_);
-  Object* object = HeapObject::FromAddress(
-      address - JSGlobalPropertyCell::kValueOffset);
-  return reinterpret_cast<JSGlobalPropertyCell*>(object);
+  return JSGlobalPropertyCell::FromValueAddress(Memory::Address_at(pc_));
 }