Add UMA for network type at request start

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 f8590d486b3abcb383de29989a2ea4fac121cc2d..1a11a972d754d8e9f430de83b472df04145af810 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -44458,6 +44458,18 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram
+    name="OfflinePages.Background.EffectiveConnectionType.OffliningStartType"
+    enum="NQEEffectiveConnectionType">
+  <owner>petewil@chromium.org</owner>
+  <summary>
+    Effective connection type at the start of an offlining attempt for an
+    attempt that eventually failed.
+
+    This metric is recorded for RequestCoordinator::SavePageLater API calls.
+  </summary>
+</histogram>
+
 <histogram name="OfflinePages.Background.EffectiveConnectionType.PauseRequests"
     enum="NQEEffectiveConnectionType">
   <owner>dougarnett@chromium.org</owner>
@@ -124261,6 +124273,8 @@ from previous Chrome versions.
   <suffix name="download" label="Offline downloaded pages"/>
   <suffix name="ntp_suggestions" label="Offline ntp suggestions"/>
   <affected-histogram
+      name="OfflinePages.Background.EffectiveConnectionType.OffliningStartType"/>
+  <affected-histogram
       name="OfflinePages.Background.EffectiveConnectionType.SavePageLater"/>
   <affected-histogram name="OfflinePages.Background.FinalSavePageResult"/>
   <affected-histogram name="OfflinePages.Background.OfflinerRequestStatus"/>