Make unload tests stable.

content/public/browser/render_widget_host.h

Index: content/public/browser/render_widget_host.h
diff --git a/content/public/browser/render_widget_host.h b/content/public/browser/render_widget_host.h
index 9ab9b0c2bda8f899f9148a03f387df5dc7ec6942..a07d82b1271e23e9f023e418e4d7f19a45bd84cf 100644
--- a/content/public/browser/render_widget_host.h
+++ b/content/public/browser/render_widget_host.h
@@ -218,6 +218,10 @@ class CONTENT_EXPORT RenderWidgetHost : public IPC::Sender {
   // 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.