Add runtime setting to force passive event listeners.

third_party/WebKit/Source/core/events/AddEventListenerOptionsDefaults.h

Index: third_party/WebKit/Source/core/events/AddEventListenerOptionsDefaults.h
diff --git a/third_party/WebKit/Source/core/events/AddEventListenerOptionsDefaults.h b/third_party/WebKit/Source/core/events/AddEventListenerOptionsDefaults.h
new file mode 100644
index 0000000000000000000000000000000000000000..20a43cdb600355364c4b54b983b9fe788cf45f2c
--- /dev/null
+++ b/third_party/WebKit/Source/core/events/AddEventListenerOptionsDefaults.h
@@ -0,0 +1,19 @@
+// 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 AddEventListenerOptionsDefaults_h
+#define AddEventListenerOptionsDefaults_h
+
+namespace blink {
+
+enum class PassiveListenerDefault {
+    False, // Default of false.

[Rick Byers, 2016/05/09 21:48:48]

Nit: make it clear this is what's required by spec.  Anything else is an
experiment which likely breaks websites.

[dtapuska, 2016/05/11 20:01:10]

Done.

+    True, // Default of true.
+    DocumentTrue, // Default of true for document level elements, false otherwise.
+    ForceAllTrue // Force all values to be true even when specified.
+};
+
+} // namespace blink
+
+#endif // AddEventListenerOptionsDefaults_h