Keep the oldest LatencyInfo when coalescing input events

Input events can be coalesced at browser side, e.g. GestureScrollUpdate,
before being sent to renderer. Currently when events are coalesced, LatencyInfo
are merged. We want to move to per-event LatencyInfo tracking and get rid
of LatencyInfo merge. It seems reasonable to keep the oldest LatencyInfo, which
when used for input event latency analysis, will represent the longest latency.

BUG=246034
TEST=None

Review URL: https://codereview.chromium.org/86603003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240160 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 6 insertions, 1 deletions

diff --git a/content/port/browser/event_with_latency_info.h b/content/port/browser/event_with_latency_info.h
index d746ce2..c0da186 100644
--- a/content/port/browser/event_with_latency_info.h
+++ b/content/port/browser/event_with_latency_info.h
@@ -36,7 +36,12 @@ class EventWithLatencyInfo {
 
   void CoalesceWith(const EventWithLatencyInfo& other) {
     WebInputEventTraits::Coalesce(other.event, &event);
-    latency.MergeWith(other.latency);
+    // When coalescing two input events, we keep the oldest LatencyInfo
+    // for Telemetry latency test since it will represent the longest
+    // latency.
+    if (other.latency.trace_id >= 0 &&
+        (latency.trace_id < 0 || other.latency.trace_id < latency.trace_id))
+      latency = other.latency;
   }
 };