Remove content::kFontListSequenceToken.

content/common/font_list_fontconfig.cc

Index: content/common/font_list_fontconfig.cc
diff --git a/content/common/font_list_fontconfig.cc b/content/common/font_list_fontconfig.cc
index 7f52829845d758bf441d632696087dbed4c5c192..3a6062d63befb2c769977ca8eba14455c3d8737c 100644
--- a/content/common/font_list_fontconfig.cc
+++ b/content/common/font_list_fontconfig.cc
@@ -26,6 +26,8 @@ std::unique_ptr<FcPattern, decltype(&FcPatternDestroy)> CreateFormatPattern(
 }
 
 std::unique_ptr<base::ListValue> GetFontList_SlowBlocking() {
+  DCHECK(GetFontListTaskRunner()->RunsTasksInCurrentSequence());
+
   std::unique_ptr<base::ListValue> font_list(new base::ListValue);
 
   std::unique_ptr<FcObjectSet, decltype(&FcObjectSetDestroy)> object_set(