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

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
===================================================================
--- chrome/common/pref_names.cc	(revision 97007)
+++ chrome/common/pref_names.cc	(working copy)
@@ -529,6 +529,14 @@
 const char kPrintingPageFooterLeft[] = "printing.page.footer.left";
 const char kPrintingPageFooterCenter[] = "printing.page.footer.center";
 const char kPrintingPageFooterRight[] = "printing.page.footer.right";
+
+// Boolean value that is set to true if print preview has been enabled once for
+// supported platforms.
+#if defined(GOOGLE_CHROME_BUILD) && !defined(OS_MACOSX) && !defined(OS_CHROMEOS)
+const char kPrintingPrintPreviewEnabledOnce[] =
+    "printing.print_preview_enabled_once";
+#endif
+
 #if defined(TOOLKIT_USES_GTK)
 // GTK specific preference on whether we should match the system GTK theme.
 const char kUsesSystemTheme[] = "extensions.theme.use_system";
@@ -1377,4 +1385,5 @@
 // Whether user-specified handlers for protocols and content types can be
 // specified.
 const char kCustomHandlersEnabled[] = "custom_handlers.enabled";
+
 }  // namespace prefs