First cut at custom user style sheets.

chrome/browser/user_style_sheet_watcher.h

Index: chrome/browser/user_style_sheet_watcher.h
diff --git a/chrome/browser/user_style_sheet_watcher.h b/chrome/browser/user_style_sheet_watcher.h
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index 0000000000000000000000000000000000000000..87fa5ce3fc1692d05179b8337e264e6ed3beec8e
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+++ b/chrome/browser/user_style_sheet_watcher.h
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+// Copyright (c) 2010 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_USER_STYLE_SHEET_WATCHER_H_
+#define CHROME_BROWSER_USER_STYLE_SHEET_WATCHER_H_
+
+#include "base/file_path.h"
+#include "base/logging.h"
+#include "base/ref_counted.h"
+#include "chrome/browser/chrome_thread.h"
+#include "chrome/common/notification_observer.h"
+#include "chrome/common/notification_registrar.h"
+#include "googleurl/src/gurl.h"
+
+// This loads the user style sheet on the file thread and sends a notification
+// when the style sheet is loaded.
+// TODO(tony): Watch for file changes and send a notification of the update.
+class UserStyleSheetWatcher
+    : public base::RefCountedThreadSafe<UserStyleSheetWatcher,
+                                        ChromeThread::DeleteOnUIThread>,
+      public NotificationObserver {
+ public:
+  explicit UserStyleSheetWatcher(const FilePath& profile_path);
+  virtual ~UserStyleSheetWatcher() {}
+
+  void Init();
+
+  GURL user_style_sheet() const {
+    return user_style_sheet_;
+  }
+
+  // NotificationObserver interface
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details);
+
+ private:
+  // Load the user style sheet on the file thread and convert it to a
+  // base64 URL.  Posts the base64 URL back to the UI thread.
+  void LoadStyleSheet(const FilePath& profile_path);
+
+  void SetStyleSheet(const GURL& url);
+
+  // The directory containing the User StyleSheet.
+  FilePath profile_path_;
+
+  // The user style sheet as a base64 data:// URL.
+  GURL user_style_sheet_;
+
+  NotificationRegistrar registrar_;
+  bool has_loaded_;
+
+  DISALLOW_COPY_AND_ASSIGN(UserStyleSheetWatcher);
+};
+
+#endif  // CHROME_BROWSER_USER_STYLE_SHEET_WATCHER_H_