Make it possible to navigate from a SkyView to a WebView.

sky/shell/ui/engine.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/shell/ui/engine.h"
 
 #include "base/bind.h"
 #include "base/trace_event/trace_event.h"
 #include "mojo/public/cpp/application/connect.h"
 #include "sky/engine/public/platform/WebInputEvent.h"
@@ skipping 167 matching lines @@
     if (web_view_) {
       web_view_->close();
       web_view_ = nullptr;
     }
     sky_view_ = blink::SkyView::Create(this);
     sky_view_->Load(url);
     UpdateSkyViewSize();
     return;
   }
 
+  if (sky_view_)
+    sky_view_ = nullptr;
+
   LOG(WARNING) << ".sky support is deprecated, please use .dart for main()";
 
   // Something bad happens if you try to call WebView::close and replace
   // the webview.  So for now we just load into the existing one. :/
   if (!web_view_)
     web_view_ = blink::WebView::create(this);
   ConfigureSettings(web_view_->settings());
   web_view_->setMainFrame(blink::WebLocalFrame::create(this));
   UpdateWebViewSize();
   web_view_->mainFrame()->load(url);
@@ skipping 43 matching lines @@
 
 void Engine::DidNavigateLocally(const mojo::String& url) {
 }
 
 void Engine::RequestNavigateHistory(int32_t delta) {
   NOTIMPLEMENTED();
 }
 
 }  // namespace shell
 }  // namespace sky