Add default constructor to the webrtc_overrides Event class.

Needed to add constructor and make use of it in webrtc, see cl
https://webrtc-review.googlesource.com/c/src/+/109500.

Bug: webrtc:9962
Change-Id: I1437a25db26ed5fa5440f5aa22daa2bdd786b73d
Reviewed-on: https://chromium-review.googlesource.com/c/1318892Reviewed-by: Henrik Grunell <grunell@chromium.org>
Commit-Queue: Niels Möller <nisse@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605984}

third_party/webrtc_overrides/rtc_base/event.cc

@@ -10,6 +10,8 @@ namespace rtc {
 
 using base::WaitableEvent;
 
+Event::Event() : Event(false, false) {}
+
 Event::Event(bool manual_reset, bool initially_signaled)
     : event_(manual_reset ? WaitableEvent::ResetPolicy::MANUAL
                           : WaitableEvent::ResetPolicy::AUTOMATIC,

third_party/webrtc_overrides/rtc_base/event.h

@@ -16,6 +16,7 @@ class Event {
  public:
   static const int kForever = -1;
 
+  Event();
   Event(bool manual_reset, bool initially_signaled);
   ~Event();
 
@@ -28,7 +29,7 @@ class Event {
 
  private:
   base::WaitableEvent event_;
-  DISALLOW_IMPLICIT_CONSTRUCTORS(Event);
+  DISALLOW_COPY_AND_ASSIGN(Event);
 };
 
 // Pull ScopedAllowBaseSyncPrimitives into the rtc namespace.