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

chrome/browser/ui/webui/prefs_internals_source.cc

+// 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.
+
+#include "chrome/browser/ui/webui/prefs_internals_source.h"
+
+#include <string>
+
+#include "base/json/json_writer.h"
+#include "base/memory/ref_counted_memory.h"
+#include "base/values.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/common/url_constants.h"
+#include "components/prefs/pref_service.h"
+#include "content/public/browser/browser_thread.h"
+
+PrefsInternalsSource::PrefsInternalsSource(Profile* profile)
+    : profile_(profile) {}
+
+PrefsInternalsSource::~PrefsInternalsSource() = default;
+
+std::string PrefsInternalsSource::GetSource() const {
+  return chrome::kChromeUIPrefsInternalsHost;
+}
+
+std::string PrefsInternalsSource::GetMimeType(const std::string& path) const {
+  return "text/plain";
+}
+
+void PrefsInternalsSource::StartDataRequest(
+    const std::string& path,
+    const content::ResourceRequestInfo::WebContentsGetter& wc_getter,
+    const content::URLDataSource::GotDataCallback& callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  std::string json;
+  std::unique_ptr<base::DictionaryValue> prefs =
+      profile_->GetPrefs()->GetPreferenceValues();
+  DCHECK(prefs);
+  CHECK(base::JSONWriter::WriteWithOptions(
+      *prefs, base::JSONWriter::OPTIONS_PRETTY_PRINT, &json));
+  callback.Run(base::RefCountedString::TakeString(&json));

[Dan Beam, 2017/03/08 18:40:58]

it probably doesn't matter, but maybe do this in the blocking pool if it takes a
long time?

[Devlin, 2017/03/20 19:25:31]

Since this is user-blocking (the user tried to load the page) and prefs are
relatively small, I think it's probably fine to do it on this thread (since the
only part we can move to the blocking pool is writing the prefs out).  If you
insist, I can move it to a blocking pool, but I'm inclined to think that you're
right about it not mattering. :)

+}