PlatformFontMac: Use a default NSFont when an invalid font is passed.

ui/gfx/render_text_unittest.cc

Index: ui/gfx/render_text_unittest.cc
diff --git a/ui/gfx/render_text_unittest.cc b/ui/gfx/render_text_unittest.cc
index 9317032a8c7828b078689089c54c6a96c70b5797..70811227531791cf97872db9aa4a0ead4f82e685 100644
--- a/ui/gfx/render_text_unittest.cc
+++ b/ui/gfx/render_text_unittest.cc
@@ -4532,11 +4532,6 @@ TEST_P(RenderTextHarfBuzzTest, GetSubstringBoundsMultiline) {
 // Tests that RenderText doesn't crash even if it's passed an invalid font. Test
 // for crbug.com/668058.
 TEST_P(RenderTextTest, InvalidFont) {
-// TODO(crbug.com/699820): This crashes with RenderTextHarfBuzz on Mac.
-#if defined(OS_MACOSX)
-  if (GetParam() == RENDER_TEXT_HARFBUZZ)
-    return;
-#endif
   const std::string font_name = "invalid_font";
   const int kFontSize = 13;
   RenderText* render_text = GetRenderText();