Bug 1383984 - Enable debugging HTMLMediaElement APIs with 'tabs' permission - r=jya,smaug

While "debugger" is not available yet, we can enable these debugging APIs for
extensions that have the "tabs" privilege, which includes the Media Panel
Devtools extension, so we/webdev will get better media-playback information.

MozReview-Commit-ID: I0MAZH9g0HU

dom/html/HTMLMediaElement.cpp

@@ -7547,10 +7547,12 @@ HTMLMediaElement::MarkAsTainted()
   }
 }
 
-bool HasDebuggerPrivilege(JSContext* aCx, JSObject* aObj)
+bool
+HasDebuggerOrTabsPrivilege(JSContext* aCx, JSObject* aObj)
 {
   return nsContentUtils::CallerHasPermission(aCx,
-                                             NS_LITERAL_STRING("debugger"));
+                                             NS_LITERAL_STRING("debugger")) ||
+         nsContentUtils::CallerHasPermission(aCx, NS_LITERAL_STRING("tabs"));
  }
 
 void