Bug 1668358 - Hide global webrtc privacy indicator on Wayland, r=emilio

The indicator never worked well on Wayland as the protocol gives us
little control about window positioning, focus etc. by design, creating
a quite bad user experience.

At the same time Wayland puts constrains on recording the display,
requiring apps to go through a "portal" where they usually have to
actively select the screen or window to share. This, crucially, allows
system compositors to show indicators itself - which all major DEs do
or at least support.

Unfortunately we can't disable the indicator at build-time as our builds
support both Wayland and X11, thus make it runtime detectable.

Differential Revision: https://phabricator.services.mozilla.com/D184193

browser/base/content/webrtcIndicator.js

@@ -73,10 +73,9 @@ const WebRTCIndicator = {
       false
     );
 
-    this.hideGlobalIndicator = Services.prefs.getBoolPref(
-      "privacy.webrtc.hideGlobalIndicator",
-      false
-    );
+    this.hideGlobalIndicator =
+      Services.prefs.getBoolPref("privacy.webrtc.hideGlobalIndicator", false) ||
+      Services.appinfo.isWayland;
 
     if (this.hideGlobalIndicator) {
       this.setVisibility(false);

toolkit/xre/nsAppRunner.cpp

@@ -1619,6 +1619,16 @@ nsXULAppInfo::GetDesktopEnvironment(nsACString& aDesktopEnvironment) {
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsXULAppInfo::GetIsWayland(bool* aResult) {
+#ifdef MOZ_WIDGET_GTK
+  *aResult = GdkIsWaylandDisplay();
+#else
+  *aResult = false;
+#endif
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 nsXULAppInfo::GetProcessStartupShortcut(nsAString& aShortcut) {
 #if defined(XP_WIN)

xpcom/system/nsIXULRuntime.idl

@@ -342,6 +342,9 @@ interface nsIXULRuntime : nsISupports
   /** Returns the desktop environment identifier. Only meaningful on GTK */
   readonly attribute ACString desktopEnvironment;
 
+  /** Whether we use Wayland. Only meaningful on GTK */
+  readonly attribute boolean isWayland;
+
   /**
    * The path of the shortcut used to start the current process, or "" if none.
    *