Remove several grab-bag includes from the v8.h header.

src/string-builder.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_STRING_BUILDER_H_
 #define V8_STRING_BUILDER_H_
 
-#include "src/v8.h"
+#include "src/objects-inl.h"
+#include "src/utils.h"
 
 namespace v8 {
 namespace internal {
 
 const int kStringBuilderConcatHelperLengthBits = 11;
 const int kStringBuilderConcatHelperPositionBits = 19;
 
 typedef BitField<int, 0, kStringBuilderConcatHelperLengthBits>
     StringBuilderSubstringLength;
 typedef BitField<int, kStringBuilderConcatHelperLengthBits,
@@ skipping 402 matching lines @@
     DCHECK_EQ(String::TWO_BYTE_ENCODING, encoding_);
     SeqTwoByteString::cast(*current_part_)
         ->SeqTwoByteStringSet(current_index_++, c);
   }
   if (current_index_ == part_length_) Extend();
 }
 }
 }  // namespace v8::internal
 
 #endif  // V8_STRING_BUILDER_H_