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

chrome/common/chrome_switches.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.
 
 // Defines all the command-line switches used by Chrome.
 
 #ifndef CHROME_COMMON_CHROME_SWITCHES_H_
 #define CHROME_COMMON_CHROME_SWITCHES_H_
 #pragma once
 
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 extern const char kClearTokenService[];
 extern const char kSetToken[];
 extern const char kWebSocketLiveExperimentHost[];
 extern const char kExposePrivateExtensionApi[];
 #endif
 
 #if defined(HAVE_XINPUT2)
 extern const char kTouchDevices[];
 #endif
 
-#if defined(GOOGLE_CHROME_BUILD) && !defined(OS_CHROMEOS) && !defined(OS_MACOSX)
 extern const char kDisablePrintPreview[];
-#else
 extern const char kEnablePrintPreview[];
-#endif
 
 bool IsPrintPreviewEnabled();
 
 bool IsInBrowserThumbnailingEnabled();
 
 // DON'T ADD RANDOM STUFF HERE. Put it in the main section above in
 // alphabetical order, or in one of the ifdefs (also in order in each section).
 
 }  // namespace switches
 
 #endif  // CHROME_COMMON_CHROME_SWITCHES_H_