PlzNavigate: Add first version of NavigationURLLoader.

content/browser/loader/navigation_url_loader_impl.h

+// Copyright 2014 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.
+
+#ifndef CONTENT_BROWSER_LOADER_NAVIGATION_URL_LOADER_IMPL_H_
+#define CONTENT_BROWSER_LOADER_NAVIGATION_URL_LOADER_IMPL_H_
+
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "content/browser/loader/navigation_url_loader.h"
+
+namespace content {
+
+class NavigationURLLoaderCore;
+
+class NavigationURLLoaderImpl : public NavigationURLLoader {
+ public:
+  // The caller is responsible for ensuring that |delegate| outlives the loader.
+  NavigationURLLoaderImpl(BrowserContext* browser_context,
+                          int64 frame_tree_node_id,
+                          const CommonNavigationParams& common_params,
+                          scoped_ptr<NavigationRequestInfo> request_info,
+                          ResourceRequestBody* request_body,
+                          NavigationURLLoader::Delegate* delegate);
+  ~NavigationURLLoaderImpl() override;
+
+  // Called in response to OnRequestRedirected to continue processing the
+  // request.
+  void FollowRedirect() override;
+
+ private:
+  friend class NavigationURLLoaderCore;
+
+  // Notifies the delegate of a redirect.
+  void NotifyRequestRedirected(const net::RedirectInfo& redirect_info,
+                               ResourceResponse* response);
+
+  // Notifies the delegate that the response has started.
+  void NotifyResponseStarted(ResourceResponse* response,
+                             scoped_ptr<StreamHandle> body);
+
+  // Notifies the delegate the request failed to return a response.
+  void NotifyRequestFailed(int net_error);
+
+  Delegate *delegate_;
+
+  // |core_| is deleted on the IO thread in a subsequent task when the
+  // |NavigationURLLoaderImpl goes out of scope.
+  NavigationURLLoaderCore* core_;

[mmenke, 2014/10/22 15:32:58]

optional:  Suggest making this a scoped_ptr - it's a bug if it's actually
deleted by the destruction of the scoped pointer, of course, but think that
makes ownership a little clearer (That comment certainly helps, too, of course).

[davidben, 2014/10/22 20:58:04]

So, I originally made it a scoped_ptr<Blah, BrowserThread::DeleteOnIOThread>.
The problem is that DeleteOnIOThread tries to be clever and breaks the unit
tests. I.e. this pattern is not actually safe:

scoped_ptr<T, DeleteOnIOThread> t(new T);
PostTask(IO, FROM_HERE, base::Bind(&DoSomething, base::Unretained(t.get()));
PostTask(IO, FROM_HERE, base::Bind(&DoSomethingElse, base::Unretained(t.get()));
t.reset();

If the current thread is not the IO thread, this works great because of PostTask
ordering. But if the current thread is the IO thread, DeleteOnIOThread is clever
and deletes the object immediately. In unit tests, UI and IO thread are aliased
to the same thread and badness ensues.

+
+  base::WeakPtrFactory<NavigationURLLoaderImpl> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(NavigationURLLoaderImpl);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_LOADER_NAVIGATION_URL_LOADER_IMPL_H_