[WebUI] Add a chrome://prefs-internals page

chrome/browser/ui/webui/prefs_internals_source.h

+// Copyright 2017 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 CHROME_BROWSER_UI_WEBUI_PREFS_INTERNALS_SOURCE_H_
+#define CHROME_BROWSER_UI_WEBUI_PREFS_INTERNALS_SOURCE_H_
+
+#include "base/macros.h"
+#include "content/public/browser/url_data_source.h"
+
+class Profile;
+
+// A simple data source that returns the preferences for the associated profile.
+class PrefsInternalsSource : public content::URLDataSource {
+ public:
+  explicit PrefsInternalsSource(Profile* profile);
+  ~PrefsInternalsSource() override;
+
+  // content::URLDataSource:
+  std::string GetSource() const override;
+  std::string GetMimeType(const std::string& path) const override;
+  void StartDataRequest(
+      const std::string& path,
+      const content::ResourceRequestInfo::WebContentsGetter& wc_getter,
+      const content::URLDataSource::GotDataCallback& callback) override;
+
+ private:
+  Profile* profile_;
+
+  DISALLOW_COPY_AND_ASSIGN(PrefsInternalsSource);
+};
+
+#endif  // CHROME_BROWSER_UI_WEBUI_PREFS_INTERNALS_SOURCE_H_