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

content/shell/renderer/test_runner/test_plugin_placeholder.h

Index: content/shell/renderer/test_runner/test_plugin_placeholder.h
diff --git a/content/shell/renderer/test_runner/test_plugin_placeholder.h b/content/shell/renderer/test_runner/test_plugin_placeholder.h
new file mode 100644
index 0000000000000000000000000000000000000000..df65ac80ae7d702d54e27eb8426da2728a0f7d86
--- /dev/null
+++ b/content/shell/renderer/test_runner/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 CONTENT_SHELL_RENDERER_TEST_RUNNER_TEST_PLUGIN_PLACEHOLDER_H_
+#define CONTENT_SHELL_RENDERER_TEST_RUNNER_TEST_PLUGIN_PLACEHOLDER_H_
+
+#include "components/plugins/renderer/plugin_placeholder.h"
+
+namespace content {
+
+// A subclass of PluginPlaceholder for use in Blink layout tests.
+class TestPluginPlaceholder : public plugins::PluginPlaceholder {
+ public:
+  TestPluginPlaceholder(blink::WebLocalFrame* frame,
+                        const blink::WebPluginParams& params);
+
+  void BindWebFrame(blink::WebFrame* frame) override {}

[tommycli, 2015/05/28 21:13:34]

This cannot be a no-op, as then this object isn't collected by V8 garbage
collection and leaks.

It's an oversight that BindWebFrame is pure virtual in PluginPlaceholder. The
two subclasses of PluginPlaceholder (LoadablePluginPlaceholder and
MobileYoutubePlugin) both implement that BindWebFrame method in the exact same
way.

You can copy their implementations into here if you want.

Otherwise, if this patch lands and sticks:
https://codereview.chromium.org/1148223004/, then this class will be
unnecessary.

[chrishtr, 2015/05/28 21:16:52]

Done.

+};
+
+}  // namespace content
+
+#endif  // CONTENT_SHELL_RENDERER_TEST_RUNNER_TEST_PLUGIN_PLACEHOLDER_H_