Add flag to disable string externalization

runtime/vm/dart_api_impl.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "include/dart_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 
 #include "platform/assert.h"
 #include "lib/stacktrace.h"
@@ skipping 41 matching lines @@
 
 
 DECLARE_FLAG(bool, print_class_table);
 DECLARE_FLAG(bool, verify_handles);
 #if defined(DART_NO_SNAPSHOT)
 DEFINE_FLAG(bool, check_function_fingerprints, true,
             "Check function fingerprints");
 #endif  // defined(DART_NO_SNAPSHOT).
 DEFINE_FLAG(bool, verify_acquired_data, false,
             "Verify correct API acquire/release of typed data.");
+DEFINE_FLAG(bool, support_externalizable_strings, true,
+            "Support Dart_MakeExternalString.");
+
 
 ThreadLocalKey Api::api_native_key_ = kUnsetThreadLocalKey;
 Dart_Handle Api::true_handle_ = NULL;
 Dart_Handle Api::false_handle_ = NULL;
 Dart_Handle Api::null_handle_ = NULL;
 Dart_Handle Api::empty_string_handle_ = NULL;
 
 
 const char* CanonicalFunction(const char* func) {
   if (strncmp(func, "dart::", 6) == 0) {
@@ skipping 2440 matching lines @@
   return Api::Success();
 }
 
 
 DART_EXPORT Dart_Handle Dart_MakeExternalString(Dart_Handle str,
                                                 void* array,
                                                 intptr_t length,
                                                 void* peer,
                                                 Dart_PeerFinalizer cback) {
   DARTSCOPE(Thread::Current());
+  if (!FLAG_support_externalizable_strings) {
+    return Api::NewError("Dart_MakeExternalString with "
+                         "--support_externalizable_strings=false");
+  }
   const String& str_obj = Api::UnwrapStringHandle(Z, str);
   if (str_obj.IsExternal()) {
     return str;  // String is already an external string.
   }
   if (str_obj.IsNull()) {
     RETURN_TYPE_ERROR(Z, str, String);
   }
   if (array == NULL) {
     RETURN_NULL_ERROR(array);
   }
@@ skipping 3581 matching lines @@
   return Api::Success();
 }
 #endif  // DART_PRECOMPILER
 
 
 DART_EXPORT bool Dart_IsRunningPrecompiledCode() {
   return Dart::IsRunningPrecompiledCode();
 }
 
 }  // namespace dart