Remove TrustedEventsDefaultAction runtime flag.

The FileManager tests have been rewritten to use browser side injection.
This feature can now be removed.

Change-Id: If9780de594d26c93f6f80ee2adf558ff5811df98
Reviewed-on: https://chromium-review.googlesource.com/c/1473404
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Navid Zolghadr <nzolghadr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#633775}

third_party/blink/renderer/core/dom/events/event_dispatcher.cc

@@ -339,9 +339,7 @@ inline void EventDispatcher::DispatchEventPostProcess(
 
   // The DOM Events spec says that events dispatched by JS (other than "click")
   // should not have their default handlers invoked.
-  bool is_trusted_or_click =
-      !RuntimeEnabledFeatures::TrustedEventsDefaultActionEnabled() ||
-      event_->isTrusted() || is_click;
+  bool is_trusted_or_click = event_->isTrusted() || is_click;
 
   // For Android WebView (distinguished by wideViewportQuirkEnabled)
   // enable untrusted events for mouse down on select elements because

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -1361,10 +1361,6 @@
       origin_trial_feature_name: "TrustedDOMTypes",
       status: "experimental",
     },
-    {
-      name: "TrustedEventsDefaultAction",
-      status: "stable",
-    },
     {
       name: "UnclosedFormControlIsInvalid",
       status: "experimental",