Add kHeaderSize constant to SeqString.

src/mips/code-stubs-mips.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 4703 matching lines @@
   __ addu(a0, a0, a2);
   __ sw(a0, MemOperand(sp, 2 * kPointerSize));
 
   // Argument 5: static offsets vector buffer.
   __ li(a0, Operand(
         ExternalReference::address_of_static_offsets_vector(masm->isolate())));
   __ sw(a0, MemOperand(sp, 1 * kPointerSize));
 
   // For arguments 4 and 3 get string length, calculate start of string data
   // and calculate the shift of the index (0 for ASCII and 1 for two byte).
-  STATIC_ASSERT(SeqAsciiString::kHeaderSize == SeqTwoByteString::kHeaderSize);
-  __ Addu(t2, subject, Operand(SeqAsciiString::kHeaderSize - kHeapObjectTag));
+  __ Addu(t2, subject, Operand(SeqString::kHeaderSize - kHeapObjectTag));
   __ Xor(a3, a3, Operand(1));  // 1 for 2-byte str, 0 for 1-byte.
   // Load the length from the original subject string from the previous stack
   // frame. Therefore we have to use fp, which points exactly to two pointer
   // sizes below the previous sp. (Because creating a new stack frame pushes
   // the previous fp onto the stack and moves up sp by 2 * kPointerSize.)
   __ lw(subject, MemOperand(fp, kSubjectOffset + 2 * kPointerSize));
   // If slice offset is not 0, load the length from the original sliced string.
   // Argument 4, a3: End of string data
   // Argument 3, a2: Start of string data
   // Prepare start and end index of the input.
@@ skipping 2285 matching lines @@
   __ mov(result, zero_reg);
   __ Ret();
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS