Wipe out isolate_ pointer after disposing it.

gin/isolate_holder.cc

 // Copyright 2013 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 "gin/public/isolate_holder.h"
 
 #include <stdlib.h>
 #include <string.h>
 
 #include "base/files/memory_mapped_file.h"
@@ skipping 236 matching lines @@
     size_t size;
     isolate_->GetCodeRange(&code_range, &size);
     Debug::CodeRangeDeletedCallback callback =
         DebugImpl::GetCodeRangeDeletedCallback();
     if (code_range && callback)
       callback(code_range);
   }
 #endif
   isolate_data_.reset();
   isolate_->Dispose();
+  isolate_ = NULL;
 }
 
 // static
 void IsolateHolder::Initialize(ScriptMode mode,
                                v8::ArrayBuffer::Allocator* allocator) {
   CHECK(allocator);
   static bool v8_is_initialized = false;
   if (v8_is_initialized)
     return;
   v8::V8::InitializePlatform(V8Platform::Get());
@@ skipping 29 matching lines @@
   base::MessageLoop::current()->AddTaskObserver(task_observer_.get());
 }
 
 void IsolateHolder::RemoveRunMicrotasksObserver() {
   DCHECK(task_observer_.get());
   base::MessageLoop::current()->RemoveTaskObserver(task_observer_.get());
   task_observer_.reset();
 }
 
 }  // namespace gin