Don't share Push API message payloads unless explicitly enabled.

content/public/common/content_switches.cc

Index: content/public/common/content_switches.cc
diff --git a/content/public/common/content_switches.cc b/content/public/common/content_switches.cc
index e8551f54cf30225d139f4dfded0e9266f352d28a..df2b0c90d829a5ebe0c7162eb24eeabfd9d968d0 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -366,6 +366,9 @@ const char kEnablePinch[]                   = "enable-pinch";
 // also applys to workers.
 const char kEnablePreciseMemoryInfo[] = "enable-precise-memory-info";
 
+// Enables payloads for received push messages when using the W3C Push API.
+const char kEnablePushMessagePayload[] = "enable-push-message-payload";
+
 // Set options to cache V8 data. (off, preparse data, or code)
 const char kV8CacheOptions[] = "v8-cache-options";