Add CompositionMarkerList in preparation for DocumentMarkerController refactor

third_party/WebKit/Source/core/editing/markers/CompositionMarkerList.cpp

Index: third_party/WebKit/Source/core/editing/markers/CompositionMarkerList.cpp
diff --git a/third_party/WebKit/Source/core/editing/markers/CompositionMarkerList.cpp b/third_party/WebKit/Source/core/editing/markers/CompositionMarkerList.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..1d34a8ca62f09bf8014d62e98c4f4dce1c519e60
--- /dev/null
+++ b/third_party/WebKit/Source/core/editing/markers/CompositionMarkerList.cpp
@@ -0,0 +1,15 @@
+// Copyright 2017 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 "core/editing/markers/CompositionMarkerList.h"
+
+namespace blink {
+
+CompositionMarkerList::CompositionMarkerList() : EditingMarkerList() {}
+
+DocumentMarker::MarkerType CompositionMarkerList::allowedMarkerType() const {
+  return DocumentMarker::Composition;
+}
+
+}  // namespace blink