Bug 1299727 - Rename NS_WARN_IF_FALSE as NS_WARNING_ASSERTION. r=erahm.

The new name makes the sense of the condition much clearer. E.g. compare:

  NS_WARN_IF_FALSE(!rv.Failed());

with:

  NS_WARNING_ASSERTION(!rv.Failed());

The new name also makes it clearer that it only has effect in debug builds,
because that's standard for assertions.

toolkit/components/url-classifier/LookupCache.cpp

@@ -207,7 +207,7 @@ LookupCache::WriteFile()
   NS_ENSURE_SUCCESS(rv, rv);
 
   rv = mPrefixSet->StoreToFile(psFile);
-  NS_WARN_IF_FALSE(NS_SUCCEEDED(rv), "failed to store the prefixset");
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "failed to store the prefixset");
 
   return NS_OK;
 }