Add option to force document level passive event listeners as a runtime feature.

content/public/common/content_features.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "build/build_config.h"
 #include "content/public/common/content_features.h"
 
 namespace features {
 
 // All features in alphabetical order.
@@ skipping 74 matching lines @@
                                   base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Paint optimizations including subsequence caching and empty phase skipping.
 const base::Feature kPaintOptimizations{"PaintOptimizations",
                                         base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Whether the lookahead parser in Blink runs on the main thread.
 const base::Feature kParseHTMLOnMainThread{"ParseHTMLOnMainThread",
                                            base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Whether document level event listeners should default 'passive' to true.
+const base::Feature kPassiveDocumentEventListeners{
+    "PassiveDocumentEventListeners", base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Pointer events support.
 const base::Feature kPointerEvents{"PointerEvent",
                                    base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Throttle Blink's rendering pipeline based on frame visibility.
 const base::Feature kRenderingPipelineThrottling{
     "RenderingPipelineThrottling", base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Scrolls to compensate for layout movements (bit.ly/scroll-anchoring).
 const base::Feature kScrollAnchoring{"ScrollAnchoring",
@@ skipping 44 matching lines @@
 #endif
 
 #if defined(OS_WIN)
 // Emergency "off switch" for new Windows sandbox security mitigation,
 // sandbox::MITIGATION_EXTENSION_POINT_DISABLE.
 const base::Feature kWinSboxDisableExtensionPoints{
     "WinSboxDisableExtensionPoint", base::FEATURE_ENABLED_BY_DEFAULT};
 #endif
 
 }  // namespace features