Fix typo in css scanner histogram macro

chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.cc

Index: chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.cc
diff --git a/chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.cc b/chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.cc
index adc54abcd938033a6e054e328b425fcfca63560e..77b74bcc7d7caa6198b2b53f6bf7a5cc371ed13e 100644
--- a/chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.cc
+++ b/chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.cc
@@ -19,7 +19,7 @@ void CssScanningMetricsObserver::OnFirstMeaningfulPaint(
       WasStartedInForegroundOptionalEventInForeground(
           timing.first_meaningful_paint, info)) {
     PAGE_LOAD_HISTOGRAM(
-        "PageLoad.Clients.CssScanner.Experimental.PaintTiming"
+        "PageLoad.Clients.CssScanner.Experimental.PaintTiming."
         "ParseStartToFirstMeaningfulPaint",
         timing.first_meaningful_paint.value() - timing.parse_start.value());
   }