Adding source_event_type to LatencyInfo mojom

ui/latency/mojo/latency_info.mojom

 // Copyright 2016 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.
 
 module ui.mojom;
 
 import "mojo/common/time.mojom";
 import "ui/gfx/geometry/mojo/geometry.mojom";
 
 enum LatencyComponentType {
@@ skipping 57 matching lines @@
   // This component indicates that the input causes a commit to be scheduled
   // but the commit was aborted since it carried no new information.
   INPUT_EVENT_LATENCY_TERMINATED_COMMIT_NO_UPDATE_COMPONENT,
   // This component indicates that the input causes a swap to be scheduled
   // but the swap failed.
   INPUT_EVENT_LATENCY_TERMINATED_SWAP_FAILED_COMPONENT,
   LATENCY_COMPONENT_TYPE_LAST =
       INPUT_EVENT_LATENCY_TERMINATED_SWAP_FAILED_COMPONENT,
 };
 
+enum SourceEventType {
+  UNKNOWN,
+  WHEEL,
+  TOUCH,
+  OTHER,
+  SOURCE_EVENT_TYPE_LAST = OTHER,

[tdresser, 2017/04/27 14:39:27]

Is there some assertion we can add to reduce the risk of these (and the
LatencyComponentType) getting out of sync with latency_info.h?

[mfomitchev, 2017/04/27 22:06:28]

What if we add an assert for ui::mojom::LATENCY_COMPONENT_TYPE_LAST matching
ui::LATENCY_COMPONENT_TYPE_LAST and a similar one for SOURCE_EVENT_TYPE_LAST in
latency_info_struct_traits.h?

tsepez@: Interested in your thoughts as well. Are we doing anything like this
elsewhere?

[Fady Samuel, 2017/04/27 22:49:25]

We deal with this problem in cc via SetAll/SetNew usage. Basically, you can't
much around with things directly

+};
+
 struct LatencyComponentId {
   LatencyComponentType type;
   int64 id;
 };
 
 struct LatencyComponent {
   // Nondecreasing number that can be used to determine what events happened
   // in the component at the time this struct was sent on to the next
   // component.
   int64 sequence_number;
@@ skipping 12 matching lines @@
   LatencyComponent value;
 };
 
 // See ui/latency/latency_info.h
 struct LatencyInfo {
   string trace_name;
   array<LatencyComponentPair> latency_components;
   int64 trace_id;
   bool coalesced;
   bool terminated;
+  SourceEventType source_event_type;
 };