Preload scan external CSS for @import

chrome/browser/chrome_content_browser_client.cc

Index: chrome/browser/chrome_content_browser_client.cc
diff --git a/chrome/browser/chrome_content_browser_client.cc b/chrome/browser/chrome_content_browser_client.cc
index 0e2ea64140eb5d5b71067c59ff6ceee1beea2bc5..e8bec119b6c61dd4f3ac3a15ed4cc195f34511b8 100644
--- a/chrome/browser/chrome_content_browser_client.cc
+++ b/chrome/browser/chrome_content_browser_client.cc
@@ -1400,6 +1400,10 @@ void MaybeAppendBlinkSettingsSwitchForFieldTrial(
     // Keys: parseHTMLOnMainThreadSyncTokenize
     //       parseHTMLOnMainThreadCoalesceChunks
     "ParseHTMLOnMainThread",
+
+    // Keys: cssExternalScannerNoPreload
+    //       cssExternalScannerPreload
+    "CSSExternalScanner",
   };
 
   std::vector<std::string> blink_settings;