Minor cleanup as saved_isolate_ should always be NULL in this case per the ASSERT in the constructo…

runtime/vm/isolate.h

 // 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.
 
 #ifndef VM_ISOLATE_H_
 #define VM_ISOLATE_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/atomic.h"
@@ skipping 894 matching lines @@
   }
 
   ~StartIsolateScope() {
     if (new_isolate_ == NULL) {
       // Do nothing.
       return;
     }
     if (saved_isolate_ != new_isolate_) {
       new_isolate_->ClearStackLimit();
       Thread::ExitIsolate();
-      if (saved_isolate_ != NULL) {
-        Thread::EnterIsolate(saved_isolate_);
-      }
+      ASSERT(saved_isolate_ == NULL);
     }
   }
 
  private:
   Isolate* new_isolate_;
   Isolate* saved_isolate_;
 
   DISALLOW_COPY_AND_ASSIGN(StartIsolateScope);
 };
 
@@ skipping 99 matching lines @@
   uint8_t* serialized_message_;
   intptr_t serialized_message_len_;
   Isolate::Flags isolate_flags_;
   bool paused_;
   bool errors_are_fatal_;
 };
 
 }  // namespace dart
 
 #endif  // VM_ISOLATE_H_