talk_base: remove lock inversion between MessageQueue and MessageQueueManager.

Removes the concept of a MessageQueue being "active" in favor of considering all
live MQ's to be active.
(previously a MQ was active starting from the first Post to it and stopped being
active in its dtor).

BUG=3230
R=sriniv@google.com

Review URL: https://webrtc-codereview.appspot.com/21489004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6190 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/talk/base/thread.cc b/talk/base/thread.cc
index d4cebc4..3fd1ca4 100644
--- a/talk/base/thread.cc
+++ b/talk/base/thread.cc
@@ -157,8 +157,7 @@
 
 Thread::~Thread() {
   Stop();
-  if (active_)
-    Clear(NULL);
+  Clear(NULL);
 }
 
 bool Thread::SleepMs(int milliseconds) {
@@ -403,7 +402,6 @@
   bool ready = false;
   {
     CritScope cs(&crit_);
-    EnsureActive();
     _SendMessage smsg;
     smsg.thread = current_thread;
     smsg.msg = msg;