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 e4580c7c456f2a166cbcde31cd93dfa8f4715559..f4762b92e03f8e22287903cfeb226adb684ef5bd 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -91500,6 +91500,8 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
     separator=".">
   <suffix name="inbox" label="Custom histogram for Inbox"/>
   <suffix name="search" label="Custom histogram for Search"/>

[falken, 2017/06/07 03:43:32]

for "the Google Search results page".

[horo, 2017/06/07 06:04:12]

Done.

+  <suffix name="search_no_sw"
+      label="Custom histogram for Search without service worker"/>

[falken, 2017/06/07 03:43:32]

This will make the label something like:
"Measures the time...for main frame documents.  PageLoadMetrics from a page that
is controlled by a Service Worker; Custom histogram for Search without service
worker"

How about:
"PageLoadMetrics from a page that is controlled by a service worker, unless
otherwise specified; Custom histogram for the Google Search results page when
NOT controlled by a service worker. The ancestor histograms above "search_no_sw"
are not recorded.

[horo, 2017/06/07 06:04:12]

Done.

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