Remove bogus CHECK in set_isolate.

sky/engine/tonic/dart_state.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sky/engine/config.h"
 #include "sky/engine/tonic/dart_state.h"
 
 #include "sky/engine/tonic/dart_class_library.h"
 #include "sky/engine/tonic/dart_converter.h"
 #include "sky/engine/tonic/dart_exception_factory.h"
@@ skipping 15 matching lines @@
       string_cache_(adoptPtr(new DartStringCache)),
       exception_factory_(adoptPtr(new DartExceptionFactory(this))),
       timer_heap_(adoptPtr(new DartTimerHeap())),
       weak_factory_(this) {
 }
 
 DartState::~DartState() {
 }
 
 void DartState::SetIsolate(Dart_Isolate isolate) {
-  CHECK(!isolate_);
   isolate_ = isolate;
   if (!isolate_)
     return;
 
   {
     Scope dart_scope(this);
     index_handle_.Set(this, ToDart("index"));
   }
 
   DidSetIsolate();
 }
 
 DartState* DartState::From(Dart_Isolate isolate) {
   return static_cast<DartState*>(Dart_IsolateData(isolate));
 }
 
 DartState* DartState::Current() {
   return static_cast<DartState*>(Dart_CurrentIsolateData());
 }
 
 base::WeakPtr<DartState> DartState::GetWeakPtr() {
   return weak_factory_.GetWeakPtr();
 }
 
 }  // namespace blink