backout Bug 559927 since suspect of causing a Windows necko test failure

netwerk/base/src/nsAsyncStreamCopier.cpp

@@ -283,12 +283,9 @@ nsAsyncStreamCopier::AsyncCopy(nsIRequestObserver *observer, nsISupports *ctx)
     // we want to receive progress notifications; release happens in
     // OnAsyncCopyComplete.
     NS_ADDREF_THIS();
-    {
-        nsAutoLock lock(mLock);
-        rv = NS_AsyncCopy(mSource, mSink, mTarget, mMode, mChunkSize,
-                          OnAsyncCopyComplete, this, mCloseSource, mCloseSink,
-                          getter_AddRefs(mCopierCtx));
-    }
+    rv = NS_AsyncCopy(mSource, mSink, mTarget, mMode, mChunkSize,
+                      OnAsyncCopyComplete, this, mCloseSource, mCloseSink,
+                      getter_AddRefs(mCopierCtx));
     if (NS_FAILED(rv)) {
         NS_RELEASE_THIS();
         Cancel(rv);