Change String::WriteUtf8() to return characters written.

src/api.cc

 // Copyright 2009 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 2621 matching lines @@
   return Utils::OpenHandle(this)->length();
 }
 
 
 int String::Utf8Length() const {
   if (IsDeadCheck("v8::String::Utf8Length()")) return 0;
   return Utils::OpenHandle(this)->Utf8Length();
 }
 
 
-int String::WriteUtf8(char* buffer, int capacity) const {
+int String::WriteUtf8(char* buffer, int capacity, int* nchars_ref) const {
   if (IsDeadCheck("v8::String::WriteUtf8()")) return 0;
   LOG_API("String::WriteUtf8");
   ENTER_V8;
   i::Handle<i::String> str = Utils::OpenHandle(this);
   StringTracker::RecordWrite(str);
   write_input_buffer.Reset(0, *str);
   int len = str->length();
   // Encode the first K - 3 bytes directly into the buffer since we
   // know there's room for them.  If no capacity is given we copy all
   // of them here.
   int fast_end = capacity - (unibrow::Utf8::kMaxEncodedSize - 1);
   int i;
   int pos = 0;
+  int nchars = 0;
   for (i = 0; i < len && (capacity == -1 || pos < fast_end); i++) {
     i::uc32 c = write_input_buffer.GetNext();
     int written = unibrow::Utf8::Encode(buffer + pos, c);
     pos += written;
+    nchars++;
   }
   if (i < len) {
     // For the last characters we need to check the length for each one
     // because they may be longer than the remaining space in the
     // buffer.
     char intermediate[unibrow::Utf8::kMaxEncodedSize];
     for (; i < len && pos < capacity; i++) {
       i::uc32 c = write_input_buffer.GetNext();
       int written = unibrow::Utf8::Encode(intermediate, c);
       if (pos + written <= capacity) {
         for (int j = 0; j < written; j++)
           buffer[pos + j] = intermediate[j];
         pos += written;
+        nchars++;
       } else {
         // We've reached the end of the buffer
         break;
       }
     }
   }
+  if (nchars_ref != NULL) *nchars_ref = nchars;
   if (i == len && (capacity == -1 || pos < capacity))
     buffer[pos++] = '\0';
   return pos;
 }
 
 
 int String::WriteAscii(char* buffer, int start, int length) const {
   if (IsDeadCheck("v8::String::WriteAscii()")) return 0;
   LOG_API("String::WriteAscii");
   ENTER_V8;
@@ skipping 1384 matching lines @@
 
 
 char* HandleScopeImplementer::Iterate(ObjectVisitor* v, char* storage) {
   HandleScopeImplementer* thread_local =
       reinterpret_cast<HandleScopeImplementer*>(storage);
   thread_local->IterateThis(v);
   return storage + ArchiveSpacePerThread();
 }
 
 } }  // namespace v8::internal