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/ref_counted.h"
+#include "content/browser/loader/navigation_url_loader.h"
+
+namespace content {
+
+class NavigationURLLoaderCore;
+
+class NavigationURLLoaderImpl : public NavigationURLLoader {

[clamy, 2014/10/13 15:22:42]

So NavigationURLLoaderImpl has really been reduced to bare bones, and it doesn't
seem to be doing much. Is there no way we could fold NavigationURLLoaderCore
into it?

[davidben, 2014/10/15 22:53:28]

It's largely so that it can be uniquely owned rather than reference-counted.
net/url_request/url_fetcher has a similar Impl/Core split.

The other option I can think of is to have Core be uniquely owned and live
entirely on the IO thread, though that wouldn't let us fold the two together.
But we could have something like...

NavigationURLLoaderImpl has
  scoped_ptr<NavigationURLLoaderCore, BrowserThread::DeleteOnIOThread> core_;
  base::WeakFactory<NavigationURLLoaderDelegate> weak_delegate_factory_;

It does PostTasks to IO thread with base::Unretained(core_.get()) in ctor and
FollowRedirect.

NavigationURLLoaderCore lives entirely on IO thread and is passed a
base::WeakPtr<Delegate> to be called on the UI thread.

NavigationURLLoaderCore again communicates with NavigationResourceHandler (which
is largely a kludge around the RDH not having a useful external API and owning
all the ResourceLoaders for you; something I want to clean up, but in parallel).
When it needs to call something on the delegate, it PostTasks back to the UI
thread with the WeakPtr.

(Really I'd like Core to be an inner class of Impl, but the ResourceHandler has
to be able to communicate with Core because of the RDH thing.)

+ 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);
+  virtual ~NavigationURLLoaderImpl();
+
+  // Called in response to OnRequestRedirected to continue processing the
+  // request.
+  virtual void FollowRedirect() override;
+
+ private:
+  scoped_refptr<NavigationURLLoaderCore> core_;
+
+  DISALLOW_COPY_AND_ASSIGN(NavigationURLLoaderImpl);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_LOADER_NAVIGATION_URL_LOADER_IMPL_H_