Make WebView::close not crash and start to fix navigation in SkyShell

sky/engine/core/script/dart_controller.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/core/script/dart_controller.h"
 
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/single_thread_task_runner.h"
@@ skipping 266 matching lines @@
     builtin_sky_->InstallWindow(dart_state());
 
     document->frame()->loaderClient()->didCreateIsolate(isolate);
 
     EnsureHandleWatcherStarted();
   }
   Dart_ExitIsolate();
 }
 
 void DartController::ClearForClose() {
-  DartIsolateScope scope(dom_dart_state_->isolate());
+  // Don't use a DartIsolateScope here since we never exit the isolate.
+  Dart_EnterIsolate(dom_dart_state_->isolate());
   Dart_ShutdownIsolate();
   dom_dart_state_.clear();
 }
 
 void DartController::InitVM() {
   int argc = 0;
   const char** argv = nullptr;
 
 #if ENABLE(ASSERT)
   argc = arraysize(kCheckedModeArgs);
   argv = kCheckedModeArgs;
 #endif
 
   CHECK(Dart_SetVMFlags(argc, argv));
   CHECK(Dart_Initialize(IsolateCreateCallback,
                         nullptr,  // Isolate interrupt callback.
                         UnhandledExceptionCallback, IsolateShutdownCallback,
                         // File IO callbacks.
                         nullptr, nullptr, nullptr, nullptr, nullptr));
 }
 
 } // namespace blink