[Offline Pages] Adds UMA for result of attempts to immediately start background loading.

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 3faf3a2d2d6ec2eb84f51204d31cf6082f9ce2e0..dac5622375b29930ae6ae5774e2a556c0ffa201f 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -38356,6 +38356,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="OfflinePages.Background.ImmediateStartStatus"
+    enum="OfflinePagesBackgroundImmediateStartStatus">
+  <owner>dougarnett@chromium.org</owner>
+  <summary>
+    Status of attempts to immediately starting background loading.

[Mark P, 2016/10/06 18:54:42]

Please clearly state when the histogram is recorded (started background loading
may be technically correct but not useful to anyone who doesn't know the
intimate details of the offline pages code).

[dougarnett, 2016/10/06 23:05:00]

Please check new wording.

+  </summary>
+</histogram>
+
 <histogram name="OfflinePages.Background.OfflinerRequestStatus"
     enum="OfflinePagesBackgroundOfflinerRequestStatus">
   <owner>dougarnett@chromium.org</owner>
@@ -91424,6 +91432,15 @@ value.
   <int value="11" label="Unknown net error, showing error page"/>
 </enum>
 
+<enum name="OfflinePagesBackgroundImmediateStartStatus" type="int">
+  <int value="0" label="Started"/>
+  <int value="1" label="Busy"/>
+  <int value="2" label="Not accepted by loader"/>
+  <int value="3" label="No connection"/>
+  <int value="4" label="No effective connection"/>
+  <int value="5" label="Not started on svelte device"/>
+</enum>
+
 <enum name="OfflinePagesBackgroundOfflinerRequestStatus" type="int">
 <!-- Generated from components/offline_pages/background/offliner.h -->