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

runtime/vm/native_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_NATIVE_ENTRY_H_
 #define VM_NATIVE_ENTRY_H_
 
 #include "platform/memory_sanitizer.h"
 
 #include "vm/allocation.h"
@@ skipping 35 matching lines @@
     CHECK_STACK_ALIGNMENT;                                                     \
     VERIFY_ON_TRANSITION;                                                      \
     NativeArguments* arguments = reinterpret_cast<NativeArguments*>(args);     \
     /* Tell MemorySanitizer 'arguments' is initialized by generated code. */   \
     MSAN_UNPOISON(arguments, sizeof(*arguments));                              \
     ASSERT(arguments->NativeArgCount() == argument_count);                     \
     TRACE_NATIVE_CALL("%s", ""#name);                                          \
     {                                                                          \
       Isolate* isolate = arguments->isolate();                                 \
       /* TODO(koda): Pivot from Isolate to Thread in NativeArguments. */       \
-      Thread* thread = Thread::CurrentFromCurrentIsolate(isolate);             \
+      Thread* thread = isolate->main_thread();                                 \
+      ASSERT(thread == Thread::Current());                                     \
       StackZone zone(isolate);                                                 \
       SET_NATIVE_RETVAL(arguments,                                             \
                         DN_Helper##name(isolate,                               \
                                         thread,                                \
                                         zone.GetZone(),                        \
                                         arguments));                           \
       DEOPTIMIZE_ALOT;                                                         \
     }                                                                          \
     VERIFY_ON_TRANSITION;                                                      \
   }                                                                            \
@@ skipping 46 matching lines @@
                                                uword pc);
   static const uint8_t* ResolveSymbol(uword pc);
   static void NativeCallWrapper(Dart_NativeArguments args,
                                 Dart_NativeFunction func);
   static const ExternalLabel& NativeCallWrapperLabel();
 };
 
 }  // namespace dart
 
 #endif  // VM_NATIVE_ENTRY_H_