Mark SVGTests::IsKnownAttribute static

Also move it be protected access.

Change-Id: I763a8112079ca3fb567b20a89c69bbfc0e420f13
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1912299
Commit-Queue: Philip Rogers <pdr@chromium.org>
Auto-Submit: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714689}

third_party/blink/renderer/core/svg/svg_tests.h

@@ -39,13 +39,13 @@ class CORE_EXPORT SVGTests : public GarbageCollectedMixin {
 
   bool IsValid() const;
 
-  bool IsKnownAttribute(const QualifiedName&);
-
   void Trace(blink::Visitor*) override;
 
  protected:
   explicit SVGTests(SVGElement* context_element);
 
+  static bool IsKnownAttribute(const QualifiedName&);
+
  private:
   Member<SVGStaticStringList> required_extensions_;
   Member<SVGStaticStringList> system_language_;