Bug 807151 - Unexport |mozilla| from the |js| namespace; r=Waldo

Clang does not want to allow js::ion::Range and mozilla::Range simultaneously
when we have a |namespace js { using namespace mozilla; }| declaration.

js/src/jsiter.cpp

@@ -50,10 +50,11 @@
 #include "vm/Stack-inl.h"
 #include "vm/String-inl.h"
 
-using namespace mozilla;
 using namespace js;
 using namespace js::gc;
 
+using mozilla::ArrayLength;
+
 static const gc::AllocKind ITERATOR_FINALIZE_KIND = gc::FINALIZE_OBJECT2;
 
 void