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

chrome/browser/browser_main.cc

Index: chrome/browser/browser_main.cc
===================================================================
--- chrome/browser/browser_main.cc	(revision 97007)
+++ chrome/browser/browser_main.cc	(working copy)
@@ -1425,6 +1425,17 @@
   if (!parsed_command_line.HasSwitch(switches::kNoErrorDialogs))
     WarnAboutMinimumSystemRequirements();
 
+  // Enable print preview once for supported platforms.
+#if defined(GOOGLE_CHROME_BUILD) && !defined(OS_MACOSX) && !defined(OS_CHROMEOS)
+  local_state->RegisterBooleanPref(prefs::kPrintingPrintPreviewEnabledOnce,
+                                   false,
+                                   PrefService::UNSYNCABLE_PREF);
+  if (!local_state->GetBoolean(prefs::kPrintingPrintPreviewEnabledOnce)) {
+    local_state->SetBoolean(prefs::kPrintingPrintPreviewEnabledOnce, true);
+    about_flags::SetExperimentEnabled(local_state, "print-preview", true);
+  }
+#endif
+
   // Convert active labs into switches. Modifies the current command line.
   about_flags::ConvertFlagsToSwitches(local_state,
                                       CommandLine::ForCurrentProcess());