Move vm_tags from isolate to thread, since we may have multiple threads in same isolate (GC, backgr…

runtime/vm/simulator_arm.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 <setjmp.h>  // NOLINT
 #include <stdlib.h>
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_ARM)
 
@@ skipping 3850 matching lines @@
   // in the previous C++ frames.
   Isolate* isolate = thread->isolate();
   StackResource::Unwind(thread);
 
   // Unwind the C++ stack and continue simulation in the target frame.
   set_register(PC, static_cast<int32_t>(pc));
   set_register(SP, static_cast<int32_t>(sp));
   set_register(FP, static_cast<int32_t>(fp));
   set_register(THR, reinterpret_cast<uword>(thread));
   // Set the tag.
-  isolate->set_vm_tag(VMTag::kDartTagId);
+  thread->set_vm_tag(VMTag::kDartTagId);
   // Clear top exit frame.
   isolate->set_top_exit_frame_info(0);
 
   ASSERT(raw_exception != Object::null());
   set_register(kExceptionObjectReg, bit_cast<int32_t>(raw_exception));
   set_register(kStackTraceObjectReg, bit_cast<int32_t>(raw_stacktrace));
   buf->Longjmp();
 }
 
 }  // namespace dart
 
 #endif  // defined(USING_SIMULATOR)
 
 #endif  // defined TARGET_ARCH_ARM