Stop unwanted class finalization when using dart:io HttpClient from builtin.dart

runtime/vm/parser.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 "vm/parser.h"
 
 #include "lib/invocation_mirror.h"
 #include "vm/bigint_operations.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
@@ skipping 4360 matching lines @@
   Dart_LibraryTagHandler handler = isolate()->library_tag_handler();
   if (handler == NULL) {
     if (url.StartsWith(Symbols::DartScheme())) {
       if (tag == Dart_kCanonicalizeUrl) {
         return url.raw();
       }
       return Object::null();
     }
     ErrorMsg(token_pos, "no library handler registered");
   }
+  // Block class finalization attempts when calling into the library
+  // tag handler.
+  isolate()->BlockClassFinalization();
   Dart_Handle result = handler(tag,
                                Api::NewHandle(isolate(), library_.raw()),
                                Api::NewHandle(isolate(), url.raw()));
+  isolate()->UnblockClassFinalization();
   if (Dart_IsError(result)) {
     // In case of an error we append an explanatory error message to the
     // error obtained from the library tag handler.
     Error& prev_error = Error::Handle();
     prev_error ^= Api::UnwrapHandle(result);
     AppendErrorMsg(prev_error, token_pos, "library handler failed");
   }
   if (tag == Dart_kCanonicalizeUrl) {
     if (!Dart_IsString(result)) {
       ErrorMsg(token_pos, "library handler failed URI canonicalization");
@@ skipping 5711 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart