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

chrome/browser/ui/webui/print_preview_ui_unittest.cc

Index: chrome/browser/ui/webui/print_preview_ui_unittest.cc
===================================================================
--- chrome/browser/ui/webui/print_preview_ui_unittest.cc	(revision 97007)
+++ chrome/browser/ui/webui/print_preview_ui_unittest.cc	(working copy)
@@ -23,9 +23,7 @@
 
 // Create/Get a preview tab for initiator tab.
 TEST_F(PrintPreviewUITest, PrintPreviewData) {
-#if !defined(GOOGLE_CHROME_BUILD) || defined(OS_CHROMEOS) || defined(OS_MACOSX)
   CommandLine::ForCurrentProcess()->AppendSwitch(switches::kEnablePrintPreview);
-#endif
   ASSERT_TRUE(browser());
   BrowserList::SetLastActive(browser());
   ASSERT_TRUE(BrowserList::GetLastActive());