Fix input and output to handle UTF16 surrogate pairs.

src/unicode.cc

Index: src/unicode.cc
===================================================================
--- src/unicode.cc	(revision 10944)
+++ src/unicode.cc	(working copy)
@@ -276,6 +276,7 @@
   return kBadChar;
 }
 
+
 const byte* Utf8::ReadBlock(Buffer<const char*> str, byte* buffer,
     unsigned capacity, unsigned* chars_read_ptr, unsigned* offset_ptr) {
   unsigned offset = *offset_ptr;
@@ -338,6 +339,16 @@
   return result;
 }
 
+unsigned CharacterStream::Utf16Length() {
+  unsigned result = 0;
+  while (has_more()) {
+    uchar c = GetNext();
+    result += c > Utf16::kMaxNonSurrogateCharCode ? 2 : 1;
+  }
+  Rewind();
+  return result;
+}
+
 void CharacterStream::Seek(unsigned position) {
   Rewind();
   for (unsigned i = 0; i < position; i++) {