Add trace events to TextFragmentAnchorMetrics.

Add trace events to help with debugging Scroll to text.

Change-Id: I98c8775365b4faa9e5206300813100902353102d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1652194Reviewed-by: David Bokan <bokan@chromium.org>
Commit-Queue: Nick Burris <nburris@chromium.org>
Cr-Commit-Position: refs/heads/master@{#668603}

third_party/blink/renderer/core/page/scrolling/text_fragment_anchor_metrics.cc

@@ -62,22 +62,42 @@ void TextFragmentAnchorMetrics::ReportMetrics() {
   }
 
   UMA_HISTOGRAM_COUNTS_100("TextFragmentAnchor.SelectorCount", selector_count_);
+  TRACE_EVENT_INSTANT1("blink", "TextFragmentAnchorMetrics::ReportMetrics",
+                       TRACE_EVENT_SCOPE_THREAD, "selector_count",
+                       selector_count_);
 
   const int match_rate_percent =
       static_cast<int>(100 * ((match_count_ + 0.0) / selector_count_));
   UMA_HISTOGRAM_PERCENTAGE("TextFragmentAnchor.MatchRate", match_rate_percent);
+  TRACE_EVENT_INSTANT1("blink", "TextFragmentAnchorMetrics::ReportMetrics",
+                       TRACE_EVENT_SCOPE_THREAD, "match_rate",
+                       match_rate_percent);
 
   UMA_HISTOGRAM_BOOLEAN("TextFragmentAnchor.AmbiguousMatch", ambiguous_match_);
+  TRACE_EVENT_INSTANT1("blink", "TextFragmentAnchorMetrics::ReportMetrics",
+                       TRACE_EVENT_SCOPE_THREAD, "ambiguous_match",
+                       ambiguous_match_);
 
   UMA_HISTOGRAM_BOOLEAN("TextFragmentAnchor.ScrollCancelled",
                         scroll_cancelled_);
+  TRACE_EVENT_INSTANT1("blink", "TextFragmentAnchorMetrics::ReportMetrics",
+                       TRACE_EVENT_SCOPE_THREAD, "scroll_cancelled",
+                       scroll_cancelled_);
 
   if (first_scroll_into_view_time_ > create_time_) {
     UMA_HISTOGRAM_BOOLEAN("TextFragmentAnchor.DidScrollIntoView",
                           did_non_zero_scroll_);
+    TRACE_EVENT_INSTANT1("blink", "TextFragmentAnchorMetrics::ReportMetrics",
+                         TRACE_EVENT_SCOPE_THREAD, "did_scroll_into_view",
+                         did_non_zero_scroll_);
 
+    WTF::TimeDelta time_to_scroll_into_view(first_scroll_into_view_time_ -
+                                            create_time_);
     UMA_HISTOGRAM_TIMES("TextFragmentAnchor.TimeToScrollIntoView",
-                        first_scroll_into_view_time_ - create_time_);
+                        time_to_scroll_into_view);
+    TRACE_EVENT_INSTANT1("blink", "TextFragmentAnchorMetrics::ReportMetrics",
+                         TRACE_EVENT_SCOPE_THREAD, "time_to_scroll_into_view",
+                         time_to_scroll_into_view.InMilliseconds());
   }
 
 #ifndef NDEBUG