Use hide_scrollbars setting for Android WebView.

android_webview/native/aw_settings.cc

Index: android_webview/native/aw_settings.cc
diff --git a/android_webview/native/aw_settings.cc b/android_webview/native/aw_settings.cc
index 8630d34575a0d35ad7c65f731c7e2509d96c1135..9bc886324bcf8164212f9297d6c13bf841e6bf33 100644
--- a/android_webview/native/aw_settings.cc
+++ b/android_webview/native/aw_settings.cc
@@ -435,6 +435,9 @@ void AwSettings::PopulateWebPreferencesLocked(JNIEnv* env,
   // possible API breakage because of disabling insecure use of geolocation.
   web_prefs->allow_geolocation_on_insecure_origins =
       Java_AwSettings_getAllowGeolocationOnInsecureOrigins(env, obj);
+
+  // We use system scrollbars, so make Blink's scrollbars invisible.
+  web_prefs->hide_scrollbars = true;
 }
 
 static jlong Init(JNIEnv* env,