LatencyInfo trace_id_ no longer dependent on sequence_number.

cc/trees/latency_info_swap_promise_monitor.cc

 // Copyright 2013 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.
 
 #include "cc/trees/latency_info_swap_promise_monitor.h"
 
 #include <stdint.h>
 
 #include "base/threading/platform_thread.h"
 #include "cc/output/latency_info_swap_promise.h"
@@ skipping 72 matching lines @@
              (reinterpret_cast<uint64_t>(this) << 32)) |
             (it->second.sequence_number & 0xffffffff);
         if (new_sequence_number == it->second.sequence_number)
           return;
         break;
       }
     }
     if (!new_sequence_number)
       return;
     ui::LatencyInfo new_latency;
+    new_latency.CopyLatencyFrom(
+        *latency_,
+        ui::INPUT_EVENT_LATENCY_FORWARD_SCROLL_UPDATE_TO_MAIN_COMPONENT);

[brianderson, 2017/06/27 18:00:58]

The new order here seems more intuitive, but how did it work before?

[tdresser, 2017/06/27 18:33:11]

Both CopyLatencyFrom and AddLatencyNumberWithTraceName just add components. An
earlier version of this required this reorder, at this point it's just cosmetic.

     new_latency.AddLatencyNumberWithTraceName(
         ui::LATENCY_BEGIN_SCROLL_LISTENER_UPDATE_MAIN_COMPONENT, 0,
         new_sequence_number, "ScrollUpdate");
-    new_latency.CopyLatencyFrom(
-        *latency_,
-        ui::INPUT_EVENT_LATENCY_FORWARD_SCROLL_UPDATE_TO_MAIN_COMPONENT);
     std::unique_ptr<SwapPromise> swap_promise(
         new LatencyInfoSwapPromise(new_latency));
     layer_tree_host_impl_->QueueSwapPromiseForMainThreadScrollUpdate(
         std::move(swap_promise));
   }
 }
 
 }  // namespace cc