Add plugins::TestPluginPlaceholder class and allow its use in Blink layout tests.

components/plugins/renderer/test_plugin_placeholder.h

Index: components/plugins/renderer/test_plugin_placeholder.h
diff --git a/components/plugins/renderer/test_plugin_placeholder.h b/components/plugins/renderer/test_plugin_placeholder.h
new file mode 100644
index 0000000000000000000000000000000000000000..bae12fa187fbc8bff3d5b41e1e0130b81ca1b939
--- /dev/null
+++ b/components/plugins/renderer/test_plugin_placeholder.h
@@ -0,0 +1,22 @@
+// 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.
+
+#ifndef COMPONENTS_PLUGINS_RENDERER_TEST_PLUGIN_PLACEHOLDER_H_
+#define COMPONENTS_PLUGINS_RENDERER_TEST_PLUGIN_PLACEHOLDER_H_
+
+#include "components/plugins/renderer/plugin_placeholder.h"
+
+namespace plugins {
+
+// A subclass of PluginPlaceholder for use in Blink layout tests.
+

[tommycli, 2015/05/26 20:08:18]

No need for blank line here

[chrishtr, 2015/05/28 20:13:56]

Done.

+class TestPluginPlaceholder : public PluginPlaceholder {
+public:

[tommycli, 2015/05/26 20:08:18]

formatting doesn't look right here. maybe git cl format?

[chrishtr, 2015/05/28 20:13:56]

Ran git cl format.

+    TestPluginPlaceholder(blink::WebLocalFrame* frame,
+                          const blink::WebPluginParams& params);
+};
+
+} // namespace plugins
+
+#endif  // COMPONENTS_PLUGINS_RENDERER_TEST_PLUGIN_PLACEHOLDER_H_