Make unload tests stable.

content/public/browser/render_widget_host.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_PUBLIC_BROWSER_RENDER_WIDGET_HOST_H_
 #define CONTENT_PUBLIC_BROWSER_RENDER_WIDGET_HOST_H_
 
 #include <stdint.h>
 
 #include "base/callback.h"
@@ skipping 200 matching lines @@
   // the size of the RenderWidget itself changing.
   virtual void ResizeRectChanged(const gfx::Rect& new_rect) = 0;
 
   // Restart the active hang monitor timeout. Clears all existing timeouts and
   // starts with a new one.  This can be because the renderer has become
   // active, the tab is being hidden, or the user has chosen to wait some more
   // to give the tab a chance to become active and we don't want to display a
   // warning too soon.
   virtual void RestartHangMonitorTimeout() = 0;
 
+  // Stops and disables hang monitor. That is needed for tests stability
+  // as under load this widget might not respond in time.

[Charlie Reis, 2016/05/23 17:03:30]

nit: Let's rephrase the second sentence:

This avoids flakiness in tests that need to observe things like beforeunload
dialogs, which could fail if the timeout skips the dialog.

+  virtual void DisableHangMonitorForTest() = 0;
+
   virtual void SetIgnoreInputEvents(bool ignore_input_events) = 0;
 
   // Called to notify the RenderWidget that it has been resized.
   virtual void WasResized() = 0;
 
   // Access to the implementation's IPC::Listener::OnMessageReceived. Intended
   // only for test code.
 
   // Add/remove a callback that can handle key presses without requiring focus.
   typedef base::Callback<bool(const NativeWebKeyboardEvent&)>
@@ skipping 13 matching lines @@
   // Get the color profile corresponding to this render widget.
   virtual bool GetScreenColorProfile(std::vector<char>* color_profile) = 0;
 
   // Sends a compositor proto to the render widget.
   virtual void HandleCompositorProto(const std::vector<uint8_t>& proto) = 0;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_RENDER_WIDGET_HOST_H_