Communicate whether passive event listeners exist to cc.

third_party/WebKit/public/platform/WebEventListenerProperties.h

+// Copyright 2016 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.
+
+#ifndef WebEventListenerProperties_h
+#define WebEventListenerProperties_h
+
+#include "WebCommon.h"
+
+namespace blink {
+
+enum class WebEventListenerClass {
+    Touch, // This value includes "pointer" events.
+    MouseWheel // This value includes "wheel" and "mousewheel" events.
+};
+
+// Indicates the variety of event listener types for a given WebEventListenerClass.
+enum class WebEventListenerProperties {
+    Nothing, // This should be "None"; but None #defined in X11's X.h
+    Passive,
+    Blocking,

[Rick Byers, 2016/02/04 22:18:57]

nit: add a comment clarifying that Blocking includes cases that also have
passive listeners.

+};
+
+} // namespace blink
+
+#endif