Add the client for accessing Subresource Filter only list.

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 72d58a4c0da5ee86f24467f740fa240fff893433..c5cf068834d8640b4147058b083c0258369b5229 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -69429,7 +69429,10 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 
 <histogram name="SubresourceFilter.PageLoad.RedirectChainLength" units="urls">
   <owner>melandory@chromium.org</owner>
-  <summary>Total length of the server redirects during the navigation.</summary>
+  <summary>
+    Total number of server redirects during the navigation. This histogram is
+    recorded in several for every list where subresource fiter is active.
+  </summary>
 </histogram>
 
 <histogram name="SubresourceFilter.PageLoad.RedirectChainMatchPattern"
@@ -69441,7 +69444,10 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
     For example, for the redirect chain A-B-C-D metric tracks: 1. If initial URL
     (A) was on a Safe Browsing blacklist. 2. If any if middle urls (B, C) were
     on a Safe Browsing blacklist. 3. If committed URL (B) was on a Safe Browsing
-    blacklist.
+    blacklist. This histogram is recorded in several flavours: with prefix
+    SubresourceFilterOnly in case the redirect chain contains url from the Safe
+    Browsing SubresourceFilter list and without the prefix for all other
+    redirect chains.
   </summary>
 </histogram>
 
@@ -123555,6 +123561,7 @@ from previous Chrome versions.
   <suffix name="SocialEngineeringAdsInterstitial"
       label="social eng ad blacklist pattern"/>
   <suffix name="PhishingInterstitial" label="phishing blacklist pattern"/>
+  <suffix name="SubresourceFilterOnly" label="subresource filter only patern"/>
   <affected-histogram name="SubresourceFilter.PageLoad.RedirectChainLength"/>
   <affected-histogram
       name="SubresourceFilter.PageLoad.RedirectChainMatchPattern"/>