Support --delete-old-versions in setup.exe.

chrome/installer/setup/setup_singleton.h

Index: chrome/installer/setup/setup_singleton.h
diff --git a/chrome/installer/setup/setup_singleton.h b/chrome/installer/setup/setup_singleton.h
index f8abc15ddb75022e8c0c79e3739fc8bc2accb929..3dd409745c636a5ab66ccc96353f32f79f0feacc 100644
--- a/chrome/installer/setup/setup_singleton.h
+++ b/chrome/installer/setup/setup_singleton.h
@@ -49,7 +49,7 @@ class SetupSingleton {
   // SetupSingleton for the same Chrome installation. In the latter case, the
   // method returns true and this SetupSingleton should be released as soon as
   // possible to unblock the other process.
-  bool WaitForInterrupt(const base::TimeDelta& max_time);
+  bool WaitForInterrupt(const base::TimeDelta& max_time) const;
 
  private:
   class ScopedHoldMutex {
@@ -79,7 +79,7 @@ class SetupSingleton {
 
   // An event signaled to ask the owner of |setup_mutex_| to release it as soon
   // as possible.
-  base::WaitableEvent exit_event_;
+  mutable base::WaitableEvent exit_event_;
 
   DISALLOW_COPY_AND_ASSIGN(SetupSingleton);
 };