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

content/shell/renderer/test_runner/web_test_delegate.h

 // Copyright 2013 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_WEB_TEST_DELEGATE_H_
 #define CONTENT_SHELL_RENDERER_TEST_RUNNER_WEB_TEST_DELEGATE_H_
 
 #include <string>
 #include <vector>
 
 #include "base/callback_forward.h"
 #include "base/memory/ref_counted.h"
 #include "third_party/WebKit/public/platform/WebScreenOrientationType.h"
 #include "third_party/WebKit/public/platform/WebString.h"
 #include "third_party/WebKit/public/platform/WebURL.h"
 #include "third_party/WebKit/public/platform/WebVector.h"
 
 #define WEBTESTRUNNER_NEW_HISTORY_CAPTURE
 
 namespace blink {
 class WebBatteryStatus;
 class WebDeviceMotionData;
 class WebDeviceOrientationData;
 class WebFrame;
 class WebGamepad;
 class WebGamepads;
 class WebHistoryItem;
 class WebLayer;
+class WebLocalFrame;
+class WebPlugin;
+struct WebPluginParams;
 class WebURLResponse;
 class WebView;
 struct WebRect;
 struct WebSize;
 struct WebURLError;
 }
 
 namespace cc {
 class TextureLayer;
 class TextureLayerClient;
@@ skipping 204 matching lines @@
       const std::vector<std::string>& event_platforms,
       const base::Callback<void(bool)>& callback) = 0;
 
   // Resolve the promise associated with the beforeinstallprompt even with
   // request id |request_id|. The promise is resolved with a result.platform set
   // to |platform|. If |platform| is not empty, result.outcome will be
   // 'accepted', otherwise it will be 'dismissed'.
   virtual void ResolveBeforeInstallPromptPromise(
       int request_id,
       const std::string& platform) = 0;
+
+  virtual blink::WebPlugin* CreatePluginPlaceholder(
+    blink::WebLocalFrame* frame,
+    const blink::WebPluginParams& params) = 0;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_SHELL_RENDERER_TEST_RUNNER_WEB_TEST_DELEGATE_H_