Add page/document timing UMAs for search without service worker

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 3c693441c30915f49c2b6f9cfb23b51caa01d1ae..39f9ef06233ee443eeee4ba0909dbaef938b22c9 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -91832,8 +91832,8 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 <histogram_suffixes name="PageLoadMetricsClientsServiceWorker" separator="."
     ordering="prefix">
   <suffix name="Clients.ServiceWorker"
-      label="PageLoadMetrics from a page that is controlled by a Service
-             Worker"/>
+      label="PageLoadMetrics from a page that is controlled by a service
+             worker, unless otherwise specified"/>
   <affected-histogram
       name="PageLoad.DocumentTiming.NavigationToDOMContentLoadedEventFired"/>
   <affected-histogram
@@ -91857,7 +91857,11 @@ 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"/>
+  <suffix name="search"
+      label="Custom histogram for the Google Search results page"/>
+  <suffix name="search_no_sw"
+      label="Custom histogram for the Google Search results page when NOT
+             controlled by a service worker"/>

[falken, 2017/06/07 06:07:29]

I think it's worth adding: "The ancestor histograms above
".search_no_sw" are not recorded."

Since we've setup histograms where:
X.Y
X.Y_a
X.Y_b
X.Y_c

When X.Y_a or X.Y_b is logged, X.Y is logged too, but when X.Y_c is logged, X.Y
is not logged.

[horo, 2017/06/07 06:32:33]

Done.

   <affected-histogram
       name="PageLoad.Clients.ServiceWorker.DocumentTiming.NavigationToDOMContentLoadedEventFired"/>
   <affected-histogram