Change VM's string-buffer patch to use a Uin16Array as backing buffer.

runtime/lib/string.cc

Index: runtime/lib/string.cc
diff --git a/runtime/lib/string.cc b/runtime/lib/string.cc
index 3b5b633a9e9802114463d9bfd90b71426f257511..48b81e96fb72e94bebc075241071b3fb7dc97098 100644
--- a/runtime/lib/string.cc
+++ b/runtime/lib/string.cc
@@ -197,4 +197,27 @@ DEFINE_NATIVE_ENTRY(Strings_concatAll, 1) {
   return String::ConcatAll(strings);
 }
 
+
+DEFINE_NATIVE_ENTRY(StringBuffer_createStringFromUint16Array, 3) {
+  GET_NON_NULL_NATIVE_ARGUMENT(Uint16Array, codeUnits,
+                               arguments->NativeArgAt(0));
+  GET_NON_NULL_NATIVE_ARGUMENT(Smi, length, arguments->NativeArgAt(1));
+  GET_NON_NULL_NATIVE_ARGUMENT(Bool, isLatin1, arguments->NativeArgAt(2));
+  intptr_t array_length = codeUnits.Length();
+  intptr_t length_value = length.Value();
+  if (length_value < 0 || length_value > array_length) {
+    const Array& args = Array::Handle(Array::New(1));
+    args.SetAt(0, length);
+    Exceptions::ThrowByType(Exceptions::kRange, args);
+  }
+  const String& result = isLatin1.value()
+      ? String::Handle(OneByteString::New(length_value, Heap::kNew))
+      : String::Handle(TwoByteString::New(length_value, Heap::kNew));
+  NoGCScope no_gc;
+
+  uint16_t* data_position = reinterpret_cast<uint16_t*>(codeUnits.ByteAddr(0));
+  String::Copy(result, 0, data_position, length_value);
+  return result.raw();
+}
+
 }  // namespace dart