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

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
===================================================================
--- chrome/browser/about_flags.cc	(revision 97007)
+++ chrome/browser/about_flags.cc	(working copy)
@@ -175,7 +175,6 @@
     kOsWin | kOsLinux | kOsCrOS,
     SINGLE_VALUE_TYPE(switches::kEnableAccelerated2dCanvas)
   },
-#if !defined(GOOGLE_CHROME_BUILD) || defined(OS_MACOSX)
   // Only expose this for Chromium builds where users may not have the PDF
   // plugin. Do not give Google Chrome users the option to disable it here,
   // except on Mac, where it is disabled.
@@ -186,7 +185,6 @@
     kOsMac | kOsWin | kOsLinux,  // This switch is not available in CrOS.
     SINGLE_VALUE_TYPE(switches::kEnablePrintPreview)
   },
-#endif
   // TODO(dspringer): When NaCl is on by default, remove this flag entry.
   {
     switches::kEnableNaCl,  // FLAGS:RECORD_UMA