desktop-pwas: Add Feature and Flag for windowing related features

This flag will be used to develop new windowing related behavior for
Desktop PWAs.

Bug: 729923
Change-Id: I594eadbdf9f00928e9c1963f510e4b7c7b7788f7
Reviewed-on: https://chromium-review.googlesource.com/566263
Commit-Queue: Giovanni Ortuño Urquidi <[email protected]>
Reviewed-by: Matt Giuca <[email protected]>
Reviewed-by: Ben Wells <[email protected]>
Cr-Commit-Position: refs/heads/master@{#485874}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 4404720f..d1bc22a 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -197,6 +197,9 @@
 extern const char kEnableDataReductionProxySavingsPromoName[];
 extern const char kEnableDataReductionProxySavingsPromoDescription[];
 
+extern const char kEnableDesktopPWAWindowingName[];
+extern const char kEnableDesktopPWAWindowingDescription[];
+
 extern const char kEnableEnumeratingAudioDevicesName[];
 extern const char kEnableEnumeratingAudioDevicesDescription[];