Ignore default namespace for rightmost compound in :not()

Mozilla has tests for this in the pipeline, although they have not
reached Blink yet:

 external/wpt/css/selectors/not-default-ns-001.html
 external/wpt/css/selectors/not-default-ns-002.html

I have verified manually that these tests now pass.

Change-Id: I4ba0e3376516afe7ca3aa6a582fbdd38b05d7cb7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2489647
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820557}

third_party/blink/renderer/core/css/parser/css_selector_parser.cc

@@ -731,6 +731,7 @@ std::unique_ptr<CSSParserSelector> CSSSelectorParser::ConsumePseudo(
       return selector;
     }
     case CSSSelector::kPseudoNot: {
+      base::AutoReset<bool> resist_namespace(&resist_default_namespace_, true);
       std::unique_ptr<CSSParserSelector> inner_selector =
           ConsumeCompoundSelector(block);
       block.ConsumeWhitespace();