Remove support for the "gcm_user_visible_only" manifest key.

content/public/common/manifest.h

Index: content/public/common/manifest.h
diff --git a/content/public/common/manifest.h b/content/public/common/manifest.h
index 59948c0b8ef513131f3594822758324f953a715f..33436e7f43b11c01a60722465f46596b8e10e2d7 100644
--- a/content/public/common/manifest.h
+++ b/content/public/common/manifest.h
@@ -117,11 +117,6 @@ struct CONTENT_EXPORT Manifest {
   // Null if parsing failed or the field was not present.
   base::NullableString16 gcm_sender_id;
 
-  // This is a proprietary extension of the web Manifest, double-check that it
-  // is okay to use this entry.
-  // False if parsing failed or the field was not present.
-  bool gcm_user_visible_only;
-
   // Maximum length for all the strings inside the Manifest when it is sent over
   // IPC. The renderer process should truncate the strings before sending the
   // Manifest and the browser process must do the same when receiving it.