Adding TryPostTask to the message loop

base/synchronization/lock.h

Index: base/synchronization/lock.h
diff --git a/base/synchronization/lock.h b/base/synchronization/lock.h
index bec37fbb3567d61ec321d23c20bf1071ddd89ba9..7e8ffe7b741bcdde1d39f69a9a123f906824a661 100644
--- a/base/synchronization/lock.h
+++ b/base/synchronization/lock.h
@@ -96,10 +96,16 @@ class BASE_EXPORT Lock {
 // A helper class that acquires the given Lock while the AutoLock is in scope.
 class AutoLock {
  public:
+  struct AlreadyAcquired {};
+
   explicit AutoLock(Lock& lock) : lock_(lock) {
     lock_.Acquire();
   }
 
+  AutoLock(Lock& lock, const AlreadyAcquired&) : lock_(lock) {
+    lock_.AssertAcquired();
+  }
+
   ~AutoLock() {
     lock_.AssertAcquired();
     lock_.Release();