viz: Add an instant trace-event for presentation.

This trace-event will be processed in telemetry for updated metrics
(see details in bug and in http://crrev.com/c/1601122)

TBR=ericrk@ for trivial change.
BUG=960824

Change-Id: Ia44316efbcd168ae61353f868f54ac6d938a1d0f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1601324Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#657781}

components/viz/service/display/display.cc

@@ -606,6 +606,9 @@ void Display::DidReceivePresentationFeedback(
   auto& callbacks = pending_presented_callbacks_.front().second;
   const auto swap_time = pending_presented_callbacks_.front().first;
   auto copy_feedback = SanitizePresentationFeedback(feedback, swap_time);
+  TRACE_EVENT_INSTANT_WITH_TIMESTAMP0(
+      "benchmark,viz", "Display::FrameDisplayed", TRACE_EVENT_SCOPE_THREAD,
+      copy_feedback.timestamp);
   for (auto& callback : callbacks) {
     std::move(callback).Run(copy_feedback);
   }