Fix error in debug printing from the Dart executable, introduced in r14357.

runtime/bin/builtin_natives.cc

Index: runtime/bin/builtin_natives.cc
diff --git a/runtime/bin/builtin_natives.cc b/runtime/bin/builtin_natives.cc
index be9b99b2b12b93e9047375585657c91255ba53fe..995207c3d2f749db2ad6f86281255af875b8e59e 100644
--- a/runtime/bin/builtin_natives.cc
+++ b/runtime/bin/builtin_natives.cc
@@ -103,11 +103,9 @@ Dart_NativeFunction Builtin::NativeLookup(Dart_Handle name,
 // test/debug functionality in standalone dart mode.
 
 void Builtin::PrintString(FILE* out, Dart_Handle str) {
-  intptr_t length = 0;
-  Dart_Handle result = Dart_StringLength(str, &length);
-  DART_CHECK_VALID(result);
-  uint8_t* chars = reinterpret_cast<uint8_t*>(malloc(length * sizeof(uint8_t)));
-  result = Dart_StringToUTF8(str, chars, &length);
+  const char* chars = NULL;
+
+  Dart_Handle result = Dart_StringToCString(str, &chars);
   if (Dart_IsError(result)) {
     // TODO(turnidge): Consider propagating some errors here.  What if
     // an isolate gets interrupted by the embedder in the middle of
@@ -115,11 +113,11 @@ void Builtin::PrintString(FILE* out, Dart_Handle str) {
     // interrupt.
     fputs(Dart_GetError(result), out);
   } else {
+    intptr_t length = strlen(chars);
     fwrite(chars, sizeof(*chars), length, out);
   }
   fputc('\n', out);
   fflush(out);
-  free(chars);
 }