Add test for ProcessSingleton hung rendezvous case.

chrome/browser/process_singleton.h

Index: chrome/browser/process_singleton.h
diff --git a/chrome/browser/process_singleton.h b/chrome/browser/process_singleton.h
index 64486881e5b0ab6b857b949f6298c334b682ad4e..60a71a7d60d877d8bb62381945fb1dbf16a5e3cc 100644
--- a/chrome/browser/process_singleton.h
+++ b/chrome/browser/process_singleton.h
@@ -92,6 +92,11 @@ class ProcessSingleton : public base::NonThreadSafe {
 #if defined(OS_POSIX) && !defined(OS_ANDROID)
   static void DisablePromptForTesting();
 #endif
+#if defined(OS_WIN)
+  typedef base::Callback<bool()> DisplayShouldKillMessageBoxCallback;
+  void OverrideKillMessageBoxCallbackForTesting(
+      const DisplayShouldKillMessageBoxCallback& display_dialog_callback);
+#endif
 
  protected:
   // Notify another process, if available.
@@ -128,6 +133,7 @@ class ProcessSingleton : public base::NonThreadSafe {
   bool is_virtualized_;  // Stuck inside Microsoft Softricity VM environment.
   HANDLE lock_file_;
   base::FilePath user_data_dir_;
+  DisplayShouldKillMessageBoxCallback display_should_kill_messagebox_callback_;
 #elif defined(OS_POSIX) && !defined(OS_ANDROID)
   // Return true if the given pid is one of our child processes.
   // Assumes that the current pid is the root of all pids of the current