desktop-pwas: Add DesktopPWAsElideExtensionsMenu flag

This CL adds a DesktopPWAsElideExtensionsMenu flag to Chrome. This is
in preparation for moving the Extensions "puzzle piece" icon out of
web app window title bars and replace it with an entry in the app menu.

Bug: 1155421
Change-Id: Idc780e77334591e1099e00dda51e20ceed488f4d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2573842
Commit-Queue: Alan Cutter <[email protected]>
Auto-Submit: Alan Cutter <[email protected]>
Reviewed-by: Eric Willigers <[email protected]>
Cr-Commit-Position: refs/heads/master@{#834104}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index daa901b..7659f2ec 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -405,6 +405,9 @@
 extern const char kDesktopPWAsAppIconShortcutsMenuName[];
 extern const char kDesktopPWAsAppIconShortcutsMenuDescription[];
 
+extern const char kDesktopPWAsElidedExtensionsMenuName[];
+extern const char kDesktopPWAsElidedExtensionsMenuDescription[];
+
 extern const char kDesktopPWAsTabStripName[];
 extern const char kDesktopPWAsTabStripDescription[];