JavaScript dialogs cause a page to lose fullscreen.

chrome/browser/printing/print_view_manager.cc

Index: chrome/browser/printing/print_view_manager.cc
diff --git a/chrome/browser/printing/print_view_manager.cc b/chrome/browser/printing/print_view_manager.cc
index 29cb6876a50f34a30b9f2c9aa9e95a1497d909be..fa54bcc082dac86618393716e52dba9b2013dc80 100644
--- a/chrome/browser/printing/print_view_manager.cc
+++ b/chrome/browser/printing/print_view_manager.cc
@@ -220,6 +220,11 @@ void PrintViewManager::OnShowScriptedPrintPreview(content::RenderFrameHost* rfh,
     return;
   }
 
+  // Running a dialog causes an exit to webpage-initiated fullscreen.
+  // http://crbug.com/728276
+  if (web_contents()->IsFullscreenForCurrentTab())
+    web_contents()->ExitFullscreen(true);
+
   dialog_controller->PrintPreview(web_contents());
   PrintHostMsg_RequestPrintPreview_Params params;
   params.is_modifiable = source_is_modifiable;