Split Thread/Isolate instances, but still maintain 1:1 relationship.

runtime/vm/runtime_entry.h

 // Copyright (c) 2011, 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.
 
 #ifndef VM_RUNTIME_ENTRY_H_
 #define VM_RUNTIME_ENTRY_H_
 
 #include "vm/allocation.h"
 #include "vm/assembler.h"
 #include "vm/flags.h"
@@ skipping 60 matching lines @@
                                Thread* thread,                                 \
                                Zone* zone,                                     \
                                NativeArguments arguments);                     \
   void DRT_##name(NativeArguments arguments) {                                 \
     CHECK_STACK_ALIGNMENT;                                                     \
     VERIFY_ON_TRANSITION;                                                      \
     ASSERT(arguments.ArgCount() == argument_count);                            \
     if (FLAG_trace_runtime_calls) OS::Print("Runtime call: %s\n", ""#name);    \
     {                                                                          \
       Isolate* isolate = arguments.isolate();                                  \
-      Thread* thread = Thread::CurrentFromCurrentIsolate(isolate);             \
+      Thread* thread = isolate->main_thread();                                 \
+      ASSERT(thread == Thread::Current());                                     \
       StackZone zone(isolate);                                                 \
       HANDLESCOPE(isolate);                                                    \
       DRT_Helper##name(isolate, thread, zone.GetZone(), arguments);            \
     }                                                                          \
     VERIFY_ON_TRANSITION;                                                      \
   }                                                                            \
   static void DRT_Helper##name(Isolate* isolate,                               \
                                Thread* thread,                                 \
                                Zone* zone,                                     \
                                NativeArguments arguments)
@@ skipping 12 matching lines @@
 
 #define END_LEAF_RUNTIME_ENTRY }
 
 #define DECLARE_LEAF_RUNTIME_ENTRY(type, name, ...)                            \
   extern const RuntimeEntry k##name##RuntimeEntry;                             \
   extern "C" type DLRT_##name(__VA_ARGS__)
 
 }  // namespace dart
 
 #endif  // VM_RUNTIME_ENTRY_H_