Bug 1037438 - implement persistent deny permissions for screen sharing, r=jesup,past.

browser/modules/webrtcUI.jsm

@@ -312,7 +312,7 @@ function prompt(aBrowser, aRequest) {
           if (audioDevices.length)
             perms.add(uri, "microphone", perms.DENY_ACTION);
           if (videoDevices.length)
-            perms.add(uri, "camera", perms.DENY_ACTION);
+            perms.add(uri, sharingScreen ? "screen" : "camera", perms.DENY_ACTION);
         }
       }
     }

dom/media/MediaManager.cpp

@@ -2265,7 +2265,8 @@ if (privileged) {
     uint32_t videoPerm = nsIPermissionManager::UNKNOWN_ACTION;
     if (IsOn(c.mVideo)) {
       rv = permManager->TestExactPermissionFromPrincipal(
-        principal, "camera", &videoPerm);
+        principal, videoType == MediaSourceEnum::Camera ? "camera" : "screen",
+        &videoPerm);
       NS_ENSURE_SUCCESS(rv, rv);
     }