Issue 6955 - Avoid making copies of common selector list

test/elemHide.js

Index: test/elemHide.js
===================================================================
--- a/test/elemHide.js
+++ b/test/elemHide.js
@@ -268,8 +268,37 @@
   ElemHide.remove(Filter.fromText("example.com##test"));
   test.equal(filtersByDomain.size, 2);
 
   ElemHide.remove(Filter.fromText("example.com,~www.example.com##test"));
   test.equal(filtersByDomain.size, 0);
 
   test.done();
 };
+
+exports.testGenericSelectorDedup = function(test)
+{
+  ElemHide.add(Filter.fromText("##test1"));
+  ElemHide.add(Filter.fromText("##test2"));
+  ElemHide.add(Filter.fromText("##test3"));
+
+  test.equal(ElemHide.getSelectorsForDomain("foo.example.com"),
+             ElemHide.getSelectorsForDomain("bar.example.com"));
+
+  ElemHide.add(Filter.fromText("foo.example.com##test4"));
+
+  test.notEqual(ElemHide.getSelectorsForDomain("foo.example.com"),
+                ElemHide.getSelectorsForDomain("bar.example.com"));
+
+  ElemHide.remove(Filter.fromText("foo.example.com##test4"));
+
+  test.equal(ElemHide.getSelectorsForDomain("foo.example.com"),
+             ElemHide.getSelectorsForDomain("bar.example.com"));
+
+  ElemHide.remove(Filter.fromText("##test1"));
+  ElemHide.remove(Filter.fromText("##test2"));
+  ElemHide.remove(Filter.fromText("##test3"));
+
+  test.equal(ElemHide.getSelectorsForDomain("foo.example.com"),
+             ElemHide.getSelectorsForDomain("bar.example.com"));
+
+  test.done();
+};