Add a base::Feature to change progress bar completion policy.

content/common/content_switches_internal.cc

Index: content/common/content_switches_internal.cc
diff --git a/content/common/content_switches_internal.cc b/content/common/content_switches_internal.cc
index eeb18a7603b40c6987a33bbfe248b5fe2591a163..105a9d193205bcc84f85e7140a79f72c21609169 100644
--- a/content/common/content_switches_internal.cc
+++ b/content/common/content_switches_internal.cc
@@ -36,6 +36,12 @@ bool IsUseZoomForDSFEnabledByDefault() {
 #endif
 }
 
+#if defined(ANDROID)
+const base::Feature kProgressBarCompletionResourcesBeforeDOMContentLoaded {
+    "progress-bar-completion-resources-before-domContentLoaded",
+    base::FEATURE_DISABLED_BY_DEFAULT};
+#endif
+
 }  // namespace
 
 bool IsPinchToZoomEnabled() {
@@ -106,6 +112,12 @@ ProgressBarCompletion GetProgressBarCompletionPolicy() {
       "resourcesBeforeDOMContentLoadedAndSameOriginIframes") {
     return ProgressBarCompletion::RESOURCES_BEFORE_DCL_AND_SAME_ORIGIN_IFRAMES;
   }
+  // The command line, which is set by the user, takes priority. Otherwise,
+  // fall back to the feature flag.
+  if (base::FeatureList::IsEnabled(
+          kProgressBarCompletionResourcesBeforeDOMContentLoaded)) {
+    return ProgressBarCompletion::RESOURCES_BEFORE_DCL;
+  }
 #endif
   return ProgressBarCompletion::LOAD_EVENT;
 }