Make WaitableEvent's constructor enum-based.

base/synchronization/waitable_event_posix.cc

Index: base/synchronization/waitable_event_posix.cc
diff --git a/base/synchronization/waitable_event_posix.cc b/base/synchronization/waitable_event_posix.cc
index 64d4376fe5654b486ea1e43cef7dc71a08fad215..08c27975126285fbf4fac41ef966165e97d969e3 100644
--- a/base/synchronization/waitable_event_posix.cc
+++ b/base/synchronization/waitable_event_posix.cc
@@ -43,6 +43,11 @@ WaitableEvent::WaitableEvent(bool manual_reset, bool initially_signaled)
     : kernel_(new WaitableEventKernel(manual_reset, initially_signaled)) {
 }
 
+WaitableEvent::WaitableEvent(ResetPolicy reset_policy,
+                             InitialState initial_state)
+    : WaitableEvent(reset_policy == ResetPolicy::MANUAL,
+                    initial_state == InitialState::SIGNALED) {}
+
 WaitableEvent::~WaitableEvent() {
 }