Report the wasted network bytes when resource prefetches hit max limit

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 149887ae400db9395f389aa4f75b2da5f6fd662e..460880394b0c52f988e66814363345a7887e4def 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -44592,6 +44592,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Precache.Fetch.ResponseBytes.NetworkWasted" units="bytes">
+  <owner>rajendrant@chromium.org</owner>
+  <owner>bengr@chromium.org</owner>
+  <summary>
+    The total number of response bytes received over the network for a wasted
+    resource prefetch. Logged when a partially downloaded resource prefetch gets

[bengr, 2016/08/26 17:15:44]

prefetch -> precache fetch

+    cancelled due to per-resource size limit or max precache size limit.
+  </summary>
+</histogram>
+
 <histogram name="Precache.Fetch.ResponseBytes.Total" units="bytes">
   <owner>twifkak@chromium.org</owner>
   <owner>bengr@chromium.org</owner>