Initialize sweeper thread array with NULL.

src/isolate.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1634 matching lines @@
       context_switcher_(NULL),
       thread_manager_(NULL),
       fp_stubs_generated_(false),
       has_installed_extensions_(false),
       string_tracker_(NULL),
       regexp_stack_(NULL),
       date_cache_(NULL),
       code_stub_interface_descriptors_(NULL),
       context_exit_happened_(false),
       deferred_handles_head_(NULL),
-      optimizing_compiler_thread_(this) {
+      optimizing_compiler_thread_(this),
+      sweeper_thread_(NULL) {
   TRACE_ISOLATE(constructor);
 
   memset(isolate_addresses_, 0,
       sizeof(isolate_addresses_[0]) * (kIsolateAddressCount + 1));
 
   heap_.isolate_ = this;
   stack_guard_.isolate_ = this;
 
   // ThreadManager is initialized early to support locking an isolate
   // before it is entered.
@@ skipping 579 matching lines @@
 
 #ifdef DEBUG
 #define ISOLATE_FIELD_OFFSET(type, name, ignored)                       \
 const intptr_t Isolate::name##_debug_offset_ = OFFSET_OF(Isolate, name##_);
 ISOLATE_INIT_LIST(ISOLATE_FIELD_OFFSET)
 ISOLATE_INIT_ARRAY_LIST(ISOLATE_FIELD_OFFSET)
 #undef ISOLATE_FIELD_OFFSET
 #endif
 
 } }  // namespace v8::internal