Refactor Thread lifecycle interface, add Thread::Enter/ExitIsolate.

runtime/vm/dart_api_impl.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_DART_API_IMPL_H_
 #define VM_DART_API_IMPL_H_
 
 #include "vm/allocation.h"
 #include "vm/native_arguments.h"
 #include "vm/object.h"
@@ skipping 273 matching lines @@
 
   friend class ApiNativeScope;
 };
 
 class IsolateSaver {
  public:
   explicit IsolateSaver(Isolate* current_isolate)
       : saved_isolate_(current_isolate) {
   }
   ~IsolateSaver() {
-    Isolate::SetCurrent(saved_isolate_);
+    // TODO(koda): Audit users; they should know whether they're in an isolate.
+    if (saved_isolate_ != NULL) {
+      Thread::EnterIsolate(saved_isolate_);
+    }
   }
  private:
   Isolate* saved_isolate_;
 
   DISALLOW_COPY_AND_ASSIGN(IsolateSaver);
 };
 
 // Start a scope in which no Dart API call backs are allowed.
 #define START_NO_CALLBACK_SCOPE(isolate)                                       \
   isolate->IncrementNoCallbackScopeDepth()
 
 // End a no Dart API call backs Scope.
 #define END_NO_CALLBACK_SCOPE(isolate)                                         \
   isolate->DecrementNoCallbackScopeDepth()
 
 #define CHECK_CALLBACK_STATE(isolate)                                          \
   if (isolate->no_callback_scope_depth() != 0) {                               \
     return reinterpret_cast<Dart_Handle>(Api::AcquiredError(isolate));         \
   }                                                                            \
 
 #define ASSERT_CALLBACK_STATE(isolate)                                         \
   ASSERT(isolate->no_callback_scope_depth() == 0)
 
 }  // namespace dart.
 
 #endif  // VM_DART_API_IMPL_H_