Print Preview: Add flag to enable the alternate UI.

This is the first step allowing to develop a componetized (with Polymer)
Print Preview UI, without affecting the existing UI during development.

Bug: 773928
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ia40f7de733d5694953175098549420f10eb1a49b
Reviewed-on: https://chromium-review.googlesource.com/717697
Commit-Queue: Demetrios Papadopoulos <[email protected]>
Reviewed-by: Lei Zhang <[email protected]>
Cr-Commit-Position: refs/heads/master@{#511344}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index bfa05cc..3308fcb 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -280,6 +280,9 @@
 extern const char kEnableNetworkServiceName[];
 extern const char kEnableNetworkServiceDescription[];
 
+extern const char kEnableNewPrintPreview[];
+extern const char kEnableNewPrintPreviewDescription[];
+
 extern const char kEnableNightLightName[];
 extern const char kEnableNightLightDescription[];