Revert of Enable HTTP/2 to use a LIFO scheduler to schedule write.

net/spdy/core/lifo_write_scheduler.h

 // Copyright (c) 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_SPDY_CORE_LIFO_WRITE_SCHEDULER_H_
 #define NET_SPDY_CORE_LIFO_WRITE_SCHEDULER_H_
 
 #include <map>
 #include <set>
 #include <tuple>
@@ skipping 51 matching lines @@
 
   StreamIdType PopNextReadyStream() override;
 
   std::tuple<StreamIdType, StreamPrecedenceType>
   PopNextReadyStreamAndPrecedence() override {
     return std::make_tuple(PopNextReadyStream(),
                            StreamPrecedenceType(kV3LowestPriority));
   }
 
   bool ShouldYield(StreamIdType stream_id) const override {
-    return !ready_streams_.empty() && stream_id < *ready_streams_.rbegin();
+    // stream_id is not necessary to be on the ready list.
+    return stream_id < *ready_streams_.rbegin();
   }
 
   void MarkStreamReady(StreamIdType stream_id, bool /*add_to_front*/) override;
 
   void MarkStreamNotReady(StreamIdType stream_id) override;
 
   bool HasReadyStreams() const override { return !ready_streams_.empty(); }
   size_t NumReadyStreams() const override { return ready_streams_.size(); }
 
  private:
@@ skipping 15 matching lines @@
 }
 
 template <typename StreamIdType>
 void LifoWriteScheduler<StreamIdType>::UnregisterStream(
     StreamIdType stream_id) {
   if (!StreamRegistered(stream_id)) {
     SPDY_BUG << "Stream " << stream_id << " is not registered";
     return;
   }
   registered_streams_.erase(stream_id);
-  ready_streams_.erase(stream_id);
 }
 
 template <typename StreamIdType>
 void LifoWriteScheduler<StreamIdType>::RecordStreamEventTime(
     StreamIdType stream_id,
     int64_t now_in_usec) {
   auto it = registered_streams_.find(stream_id);
   if (it != registered_streams_.end()) {
     it->second = now_in_usec;
   } else {
@@ skipping 35 matching lines @@
 }
 
 template <typename StreamIdType>
 void LifoWriteScheduler<StreamIdType>::MarkStreamReady(StreamIdType stream_id,
                                                        bool /*add_to_front*/) {
   if (!StreamRegistered(stream_id)) {
     SPDY_BUG << "Stream " << stream_id << " is not registered";
     return;
   }
   if (ready_streams_.find(stream_id) != ready_streams_.end()) {
-    VLOG(1) << "Stream already exists in the list";
+    SPDY_BUG << "Stream already exists in the list";
     return;
   }
   ready_streams_.insert(stream_id);
 }
 
 template <typename StreamIdType>
 void LifoWriteScheduler<StreamIdType>::MarkStreamNotReady(
     StreamIdType stream_id) {
   auto it = ready_streams_.find(stream_id);
   if (it == ready_streams_.end()) {
-    VLOG(1) << "Try to remove a stream that is not on list";
+    SPDY_BUG << "Try to remove a stream that is not on list";
     return;
   }
   ready_streams_.erase(it);
 }
 
 }  // namespace net
 
 #endif  // NET_SPDY_CORE_LIFO_WRITE_SCHEDULER_H_