[Merge to M60] Add UMA for ServiceWorker FirstMeaningfulPaint

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 94d9ea6df48017d131abe21e15c0a2076375da8b..c5e9e9b3a1ee37ab3f6054427fc866a04355c7d2 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -91568,6 +91568,10 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
       name="PageLoad.DocumentTiming.NavigationToDOMContentLoadedEventFired"/>
   <affected-histogram
       name="PageLoad.DocumentTiming.NavigationToLoadEventFired"/>
+  <affected-histogram
+      name="PageLoad.Experimental.PaintTiming.NavigationToFirstMeaningfulPaint"/>
+  <affected-histogram
+      name="PageLoad.Experimental.PaintTiming.ParseStartToFirstMeaningfulPaint"/>
   <affected-histogram
       name="PageLoad.PaintTiming.NavigationToFirstContentfulPaint"/>
   <affected-histogram
@@ -91583,10 +91587,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 <histogram_suffixes name="PageLoadMetricsClientsServiceWorkerSpecialApps"
     separator=".">
   <suffix name="inbox" label="Custom histogram for Inbox"/>
+  <suffix name="search" label="Custom histogram for Search"/>
   <affected-histogram
       name="PageLoad.Clients.ServiceWorker.DocumentTiming.NavigationToDOMContentLoadedEventFired"/>
   <affected-histogram
       name="PageLoad.Clients.ServiceWorker.DocumentTiming.NavigationToLoadEventFired"/>
+  <affected-histogram
+      name="PageLoad.Clients.ServiceWorker.Experimental.PaintTiming.NavigationToFirstMeaningfulPaint"/>
+  <affected-histogram
+      name="PageLoad.Clients.ServiceWorker.Experimental.PaintTiming.ParseStartToFirstMeaningfulPaint"/>
   <affected-histogram
       name="PageLoad.Clients.ServiceWorker.PaintTiming.NavigationToFirstContentfulPaint"/>
   <affected-histogram