Make PendingTask move-only and pass it by value on retaining params

base/stl_util.h

Index: base/stl_util.h
diff --git a/base/stl_util.h b/base/stl_util.h
index 12e226a9db9b106b95f9500efe684463d1ecd1f2..aa8a6f948a067df6f63a964632286afbae04c012 100644
--- a/base/stl_util.h
+++ b/base/stl_util.h
@@ -257,6 +257,15 @@ bool STLIncludes(const Arg1& a1, const Arg2& a2) {
                        a2.begin(), a2.end());
 }
 
+template <typename PriorityQueue>
+typename PriorityQueue::value_type
+PopOutFromPriorityQueue(PriorityQueue* queue) {
+  using ValueType = typename PriorityQueue::value_type;
+  ValueType ret = std::move(const_cast<ValueType&>(queue->top()));
+  queue->pop();
+  return ret;
+}
+
 }  // namespace base
 
 #endif  // BASE_STL_UTIL_H_