Reduce the scope of rtc::Event::Wait() locking.

webrtc/base/event.cc

Index: webrtc/base/event.cc
diff --git a/webrtc/base/event.cc b/webrtc/base/event.cc
index a9af20863194c02de5a9234b20966f60089c24ca..0e267dc1ac31a0743613650233229a0e6a12e6d0 100644
--- a/webrtc/base/event.cc
+++ b/webrtc/base/event.cc
@@ -79,14 +79,13 @@ void Event::Reset() {
 }
 
 bool Event::Wait(int milliseconds) {
-  pthread_mutex_lock(&event_mutex_);
   int error = 0;
 
+  struct timespec ts;
   if (milliseconds != kForever) {
     // Converting from seconds and microseconds (1e-6) plus
     // milliseconds (1e-3) to seconds and nanoseconds (1e-9).
 
-    struct timespec ts;
 #if HAVE_PTHREAD_COND_TIMEDWAIT_RELATIVE
     // Use relative time version, which tends to be more efficient for
     // pthread implementations where provided (like on Android).
@@ -105,7 +104,10 @@ bool Event::Wait(int milliseconds) {
       ts.tv_nsec -= 1000000000;
     }
 #endif
+  }
 
+  pthread_mutex_lock(&event_mutex_);

[tommi, 2016/02/19 16:40:42]

There's a slight change in behavior because of this.
With the patch the timeout *includes* the time it takes to wait for
event_mutex_, but without it, the cost of acquiring event_mutex_ is not counted
as part of doing the actual wait.
Maybe that does matter, maybe not, but we need to keep an eye on it.

+  if (milliseconds != kForever) {
     while (!event_status_ && error == 0) {
 #if HAVE_PTHREAD_COND_TIMEDWAIT_RELATIVE
       error = pthread_cond_timedwait_relative_np(