Back out bug 760342 for Windows build error, bug 755070 for Android crashes, and bug 760458 because it depends on 755070

js/src/jsweakmap.h

@@ -187,6 +187,7 @@ class WeakMap : public HashMap<Key, Value, HashPolicy, RuntimeAllocPolicy>, publ
                     markedAny = true;
                 e.rekeyFront(k);
             }
+            JS_ASSERT_IF(keyIsMarked, gc::IsMarked(&e.front().value));
         }
         return markedAny;
     }