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

components/plugins/renderer/test_plugin_placeholder.cc

Index: components/plugins/renderer/test_plugin_placeholder.cc
diff --git a/components/plugins/renderer/test_plugin_placeholder.cc b/components/plugins/renderer/test_plugin_placeholder.cc
new file mode 100644
index 0000000000000000000000000000000000000000..73abf3b43406a096476fb54c9d5644e99bc0901b
--- /dev/null
+++ b/components/plugins/renderer/test_plugin_placeholder.cc
@@ -0,0 +1,14 @@
+// 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.
+
+#include "components/plugins/renderer/test_plugin_placeholder.h"
+
+namespace plugins {
+
+TestPluginPlaceholder::TestPluginPlaceholder(
+    blink::WebLocalFrame* frame, const blink::WebPluginParams& params)
+    : PluginPlaceholder(nullptr, frame, params, "<div>Test content</div>")

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

Can we just eliminate this class entirely? Why not just create a
PluginPlaceholder with the <div>Test content</div> html_data in your test code?

[chrishtr, 2015/05/26 20:52:36]

The reason is that someone has to include the string of HTML. Maybe I can
extract that from the child nodes of the containing <embed> tag, will try that.
It would be great for the layout test to easily specify plugin webview content
itself.

[tommycli, 2015/05/26 21:18:02]

Perhaps I am misunderstanding something. Can "<div>Test content</div>" just be a
string literal within web_test_proxy.cc?

+{ }
+
+}  // namespace plugins