Fix windows build (static_cast missing).

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"
 
 namespace v8 {
@@ skipping 307 matching lines @@
       }
       cursor_ = start_;
     }
 
     INLINE(void Append(DestChar c)) { *(cursor_++) = c; }
     INLINE(void AppendCString(const char* s)) {
       const uint8_t* u = reinterpret_cast<const uint8_t*>(s);
       while (*u != '\0') Append(*(u++));
     }
 
-    int written() { return cursor_ - start_; }
+    int written() { return static_cast<int>(cursor_ - start_); }
 
    private:
     DestChar* start_;
     DestChar* cursor_;
     DisallowHeapAllocation no_gc_;
   };
 
   template <typename DestChar>
   class NoExtendString : public NoExtend<DestChar> {
    public:
@@ skipping 82 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_