Bug 1225923 - part 5 - fix AppendElement(nsDependentAtomString(...)) calls; r=bz

The intent here is to copy the dependent string.  We can make that
behavior more explicit by using the ToString method of nsIAtom instead.

dom/html/HTMLOptionsCollection.cpp

@@ -309,9 +309,10 @@ HTMLOptionsCollection::GetSupportedNames(unsigned aFlags,
     }
   }
 
-  aNames.SetCapacity(atoms.Length());
-  for (uint32_t i = 0; i < atoms.Length(); ++i) {
-    aNames.AppendElement(nsDependentAtomString(atoms[i]));
+  uint32_t atomsLen = atoms.Length();
+  nsString* names = aNames.AppendElements(atomsLen);
+  for (uint32_t i = 0; i < atomsLen; ++i) {
+    atoms[i]->ToString(names[i]);
   }
 }