Add kHeaderSize constant to SeqString.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 72ec0d4318f758096d6302342783b8dcf2384315..3be92184c8fb58568afb7ed722a6d89df63b08ca 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -6130,6 +6130,9 @@ class SeqString: public String {
   // Casting.
   static inline SeqString* cast(Object* obj);
 
+  // Layout description.
+  static const int kHeaderSize = String::kSize;
+
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(SeqString);
 };
@@ -6163,10 +6166,6 @@ class SeqAsciiString: public SeqString {
     return OBJECT_POINTER_ALIGN(kHeaderSize + length * kCharSize);
   }
 
-  // Layout description.
-  static const int kHeaderSize = String::kSize;
-  static const int kAlignedSize = POINTER_SIZE_ALIGN(kHeaderSize);
-
   // Maximal memory usage for a single sequential ASCII string.
   static const int kMaxSize = 512 * MB - 1;
   // Maximal length of a single sequential ASCII string.
@@ -6217,10 +6216,6 @@ class SeqTwoByteString: public SeqString {
     return OBJECT_POINTER_ALIGN(kHeaderSize + length * kShortSize);
   }
 
-  // Layout description.
-  static const int kHeaderSize = String::kSize;
-  static const int kAlignedSize = POINTER_SIZE_ALIGN(kHeaderSize);
-
   // Maximal memory usage for a single sequential two-byte string.
   static const int kMaxSize = 512 * MB - 1;
   // Maximal length of a single sequential two-byte string.