Add a NavigationThrottle to the public content/ interface

content/browser/frame_host/navigation_handle_factory.h

Index: content/browser/frame_host/navigation_handle_factory.h
diff --git a/content/browser/frame_host/navigation_handle_factory.h b/content/browser/frame_host/navigation_handle_factory.h
new file mode 100644
index 0000000000000000000000000000000000000000..5e89baa958c0ce2d89ac6c15588a2b7bf0c71b53
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+++ b/content/browser/frame_host/navigation_handle_factory.h
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+// 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.
+
+#ifndef CONTENT_BROWSER_FRAME_HOST_NAVIGATION_HANDLE_FACTORY_H_
+#define CONTENT_BROWSER_FRAME_HOST_NAVIGATION_HANDLE_FACTORY_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "url/gurl.h"
+
+namespace content {
+
+class NavigationHandleImpl;
+class NavigatorDelegate;
+
+// This class is used to create NavigationHandles through a static method.
+// Normally it creates regular NavigationHandleImpls. However, a global
+// instance of this interface can be registered through SetFactoryForTesting.
+// In that case, NavigationHandleFactory::Create will use the CreateHandle
+// method of the registered interface to create NavigationHandles. This is used
+// in unit tests to create TestNavigationHandles instead of plain
+// NavigationHandleImpls.
+class NavigationHandleFactory {
+ public:
+  // Returs a NavigationHandle. This is a plain NavigationHandleImpl, unless a
+  // factory has been registered for testing.
+  static scoped_ptr<NavigationHandleImpl> Create(const GURL& url,
+                                                 bool is_main_frame,
+                                                 NavigatorDelegate* delegate);
+
+  // Registers a factory during tests. NavigationHandleFactory::Create will
+  // then return the result of factory->CreateHandle, if |factory| is not null.
+  // Otherwise it will continue returning plain NavigationHandleImpls.
+  static void SetFactoryForTesting(NavigationHandleFactory* factory);
+
+  virtual ~NavigationHandleFactory();
+
+  // When a factory is registered, this method will be used to create
+  // NavigationHandles.
+  virtual scoped_ptr<NavigationHandleImpl> CreateHandle(
+      const GURL& url,
+      bool is_main_frame,
+      NavigatorDelegate* delegate) = 0;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_FRAME_HOST_NAVIGATION_HANDLE_FACTORY_H_