Introduce WebPluginContainerBase to abstract WebPluginContainerImpl.

third_party/WebKit/Source/core/exported/WebPluginContainerBase.cpp

Index: third_party/WebKit/Source/core/exported/WebPluginContainerBase.cpp
diff --git a/third_party/WebKit/Source/core/exported/WebPluginContainerBase.cpp b/third_party/WebKit/Source/core/exported/WebPluginContainerBase.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..8b8f591f72d30fd4c97d64557df0a7dabebf28a8
--- /dev/null
+++ b/third_party/WebKit/Source/core/exported/WebPluginContainerBase.cpp
@@ -0,0 +1,17 @@
+// 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.#ifndef WebViewBase_h
+
+#include "core/exported/WebPluginContainerBase.h"
+
+namespace blink {
+
+WebPluginContainerBase::WebPluginContainerBase(LocalFrame* frame)
+    : ContextClient(frame) {}
+
+DEFINE_TRACE(WebPluginContainerBase) {
+  ContextClient::Trace(visitor);
+  PluginView::Trace(visitor);
+}
+
+}  // namespace blink