Print Preview: Add "print preview" back to about:flags; enable it by default just once.

chrome/common/pref_names.h

 // Copyright (c) 2011 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.
 
 // Constants for the names of various preferences, for easier changing.
 
 #ifndef CHROME_COMMON_PREF_NAMES_H_
 #define CHROME_COMMON_PREF_NAMES_H_
 #pragma once
 
@@ skipping 171 matching lines @@
 extern const char kEnableAutoSpellCorrect[];
 extern const char kSavingBrowserHistoryDisabled[];
 extern const char kDeleteTimePeriod[];
 extern const char kPrintingEnabled[];
 extern const char kPrintingPageHeaderLeft[];
 extern const char kPrintingPageHeaderCenter[];
 extern const char kPrintingPageHeaderRight[];
 extern const char kPrintingPageFooterLeft[];
 extern const char kPrintingPageFooterCenter[];
 extern const char kPrintingPageFooterRight[];
+
+#if defined(GOOGLE_CHROME_BUILD) && !defined(OS_MACOSX) && !defined(OS_CHROMEOS)
+extern const char kPrintingPrintPreviewEnabledOnce[];
+#endif
+
 #if defined(TOOLKIT_USES_GTK)
 extern const char kUsesSystemTheme[];
 #endif
 extern const char kCurrentThemePackFilename[];
 extern const char kCurrentThemeID[];
 extern const char kCurrentThemeImages[];
 extern const char kCurrentThemeColors[];
 extern const char kCurrentThemeTints[];
 extern const char kCurrentThemeDisplayProperties[];
 extern const char kExtensionsUIDeveloperMode[];
@@ skipping 301 matching lines @@
 extern const char kRegisteredProtocolHandlers[];
 extern const char kIgnoredProtocolHandlers[];
 extern const char kCustomHandlersEnabled[];
 
 extern const char kUserCreatedLoginItem[];
 extern const char kBackgroundModeEnabled[];
 
 }  // namespace prefs
 
 #endif  // CHROME_COMMON_PREF_NAMES_H_