[orca] Sanity check window:activate events from Gecko before setting active script

[Joanmarie Diggs <joanied src gnome org>]

commit 412a829c9786129e5d56c47f6d7a05fb79470934
Author: Joanmarie Diggs <jdiggs igalia com>
Date:   Tue Feb 7 07:28:06 2017 -0500

    Sanity check window:activate events from Gecko before setting active script

 src/orca/scripts/toolkits/Gecko/script.py |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/src/orca/scripts/toolkits/Gecko/script.py b/src/orca/scripts/toolkits/Gecko/script.py
index 10e96c5..1107b65 100644
--- a/src/orca/scripts/toolkits/Gecko/script.py
+++ b/src/orca/scripts/toolkits/Gecko/script.py
@@ -56,6 +56,12 @@ class Script(web.Script):
 
         return Utilities(self)
 
+    def isActivatableEvent(self, event):
+        if event.type == "window:activate":
+            return self.utilities.canBeActiveWindow(event.source)
+
+        return super().isActivatableEvent(event)
+
     def locusOfFocusChanged(self, event, oldFocus, newFocus):
         """Handles changes of focus of interest to the script."""