Remove BrowserPlugin tests (only one test remaining with existing coverage)

content/renderer/browser_plugin/mock_browser_plugin.h

-// Copyright (c) 2012 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_RENDERER_BROWSER_PLUGIN_MOCK_BROWSER_PLUGIN_H_
-#define CONTENT_RENDERER_BROWSER_PLUGIN_MOCK_BROWSER_PLUGIN_H_
-
-#include "content/renderer/browser_plugin/browser_plugin.h"
-
-namespace content {
-
-class MockBrowserPlugin : public BrowserPlugin {
- public:
-  MockBrowserPlugin(RenderViewImpl* render_view,
-                    blink::WebFrame* frame,
-                    scoped_ptr<BrowserPluginDelegate> delegate);
-
-  virtual ~MockBrowserPlugin();
-
-  // Allow poking at a few private members.
-  using BrowserPlugin::OnAttachACK;
-  using BrowserPlugin::guest_crashed_;
-};
-
-}  // namespace content
-
-#endif  // CONTENT_RENDERER_BROWSER_PLUGIN_MOCK_BROWSER_PLUGIN_H_