Ensure double alignment when deserializing.

src/serialize.h

Index: src/serialize.h
diff --git a/src/serialize.h b/src/serialize.h
index 1c781139b5a6a0cf1092261bcaff9ffc15247913..94e05eb8cd3d55ebb10152258f118b30f791d604 100644
--- a/src/serialize.h
+++ b/src/serialize.h
@@ -301,20 +301,20 @@ class SerializerDeserializer: public ObjectVisitor {
  protected:
   // Where the pointed-to object can be found:
   enum Where {
-    kNewObject = 0,  // Object is next in snapshot.
-    // 1-7                             One per space.
+    kNewObject = 0,  //              Object is next in snapshot.
+    // 1-7                           One per space.
     kRootArray = 0x9,             // Object is found in root array.
     kPartialSnapshotCache = 0xa,  // Object is in the cache.
     kExternalReference = 0xb,     // Pointer to an external reference.
     kSkip = 0xc,                  // Skip n bytes.
     kBuiltin = 0xd,               // Builtin code object.
     kAttachedReference = 0xe,     // Object is described in an attached list.
-    kNop = 0xf,                   // Does nothing, used to pad.
-    kBackref = 0x10,              // Object is described relative to end.
-    // 0x11-0x17                       One per space.
-    kBackrefWithSkip = 0x18,  // Object is described relative to end.
-    // 0x19-0x1f                       One per space.
-    // 0x20-0x3f                       Used by misc. tags below.
+    // 0xf                           Used by misc. See below.
+    kBackref = 0x10,  //             Object is described relative to end.
+    // 0x11-0x17                     One per space.
+    kBackrefWithSkip = 0x18,  //     Object is described relative to end.
+    // 0x19-0x1f                     One per space.
+    // 0x20-0x3f                     Used by misc. See below.
     kPointedToMask = 0x3f
   };
 
@@ -375,6 +375,9 @@ class SerializerDeserializer: public ObjectVisitor {
     return byte_code & 0x1f;
   }
 
+  static const int kNop = 0xf;                 // Do nothing, used for padding.
+  static const int kDoubleAlignPrefix = 0x4f;  // Double align next object.
+
   static const int kAnyOldSpace = -1;
 
   // A bitmask for getting the space out of an instruction.
@@ -437,7 +440,7 @@ class Deserializer: public SerializerDeserializer {
   // the heap.
   void ReadData(Object** start, Object** end, int space,
                 Address object_address);
-  void ReadObject(int space_number, Object** write_back);
+  void ReadObject(int space_number, Object** write_back, bool double_align);
   Address Allocate(int space_index, int size);
 
   // Special handling for serialized code like hooking up internalized strings.