Implement safepointing of threads

runtime/lib/isolate.cc

 // Copyright (c) 2012, 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_native_api.h"
 #include "platform/assert.h"
 #include "vm/bootstrap_natives.h"
 #include "vm/class_finalizer.h"
 #include "vm/dart.h"
 #include "vm/dart_api_impl.h"
@@ skipping 280 matching lines @@
 
 static const char* CanonicalizeUri(Thread* thread,
                                    const Library& library,
                                    const String& uri,
                                    char** error) {
   const char* result = NULL;
   Zone* zone = thread->zone();
   Isolate* isolate = thread->isolate();
   Dart_LibraryTagHandler handler = isolate->library_tag_handler();
   if (handler != NULL) {
+    TransitionVMToNative transition(thread);
     Dart_EnterScope();
     Dart_Handle handle = handler(Dart_kCanonicalizeUrl,
                                  Api::NewHandle(thread, library.raw()),
                                  Api::NewHandle(thread, uri.raw()));
     const Object& obj = Object::Handle(Api::UnwrapHandle(handle));
     if (obj.IsString()) {
       result = String2UTF8(String::Cast(obj));
     } else if (obj.IsError()) {
       Error& error_obj = Error::Handle();
       error_obj ^= obj.raw();
@@ skipping 134 matching lines @@
   MessageWriter writer(&data, &allocator, false);
   writer.WriteMessage(msg);
 
   PortMap::PostMessage(new Message(port.Id(),
                                    data, writer.BytesWritten(),
                                    Message::kOOBPriority));
   return Object::null();
 }
 
 }  // namespace dart