Add a feature flag for enabling transparent doodle request.

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 923c1c346bf128d1342858bb0be45781fc6e08d0..cb12f7430d7edcbe073d600f2408f6bd4f2a667f 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1773,6 +1773,13 @@ const FeatureEntry kFeatureEntries[] = {
      IDS_FLAGS_ENABLE_NTP_SNIPPETS_DESCRIPTION, kOsAndroid,
      FEATURE_VALUE_TYPE(chrome::android::kNTPSnippetsFeature)},
 #endif  // defined(OS_ANDROID)
+#if defined(OS_ANDROID)
+     {"enable-ntp-transparent-doodle",
+      IDS_FLAGS_ENABLE_NTP_TRANSPARENT_DOODLE_NAME,
+      IDS_FLAGS_ENABLE_NTP_TRANSPARENT_DOODLE_DESCRIPTION,
+      kOsAndroid,
+      FEATURE_VALUE_TYPE(chrome::android::kNTPTransparentDoodle)},
+#endif // defined(OS_ANDROID)
 #if defined(ENABLE_WEBRTC) && BUILDFLAG(RTC_USE_H264)
     {"enable-webrtc-h264-with-openh264-ffmpeg",
      IDS_FLAGS_WEBRTC_H264_WITH_OPENH264_FFMPEG_NAME,