Add new UMA to record the bytes wasted due to download resumption

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 8b647fa873307b769a21dc340e6f20e555187554..11b41ec72bbd7438926936147c499ba40bc56cea 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -27974,6 +27974,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="MobileDownload.BytesWasted" units="KB">

[Ilya Sherman, 2017/02/08 02:11:19]

nit: Please add the attribute base="true"

[qinmin, 2017/02/09 01:05:11]

Done.

+  <owner>qinmin@chromium.org</owner>
+  <summary>
+    Android: Records the total data wasted during download due to resumptions.
+  </summary>
+</histogram>
+
 <histogram name="MobileDownload.CancelReason" enum="MobileDownloadCancelReason">
   <owner>qinmin@chromium.org</owner>
   <summary>Android: Records the reason that a download is canceled.</summary>
@@ -113873,6 +113880,13 @@ value.
   <affected-histogram name="MobileDownload.BytesDownloaded"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="MobileDownloadBytesWastedTypes" separator=".">
+  <suffix name="ChromeNetworkStack.Failure"/>

[Ilya Sherman, 2017/02/08 02:11:19]

nit: Please add a label like "Recorded upon download failure."

[qinmin, 2017/02/09 01:05:11]

Done.

+  <suffix name="ChromeNetworkStack.Success"/>
+  <suffix name="ChromeNetworkStack.Cancel"/>

[Ilya Sherman, 2017/02/08 02:11:19]

nit: Why not include "ChromeNetworkStack" in the histogram base histogram name?

[qinmin, 2017/02/09 01:05:11]

Done.

+  <affected-histogram name="MobileDownload.BytesWasted"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="MobileDownloadDownloadTimeTypes" separator=".">
   <suffix name="ChromeNetworkStack.Cancel"/>
   <suffix name="ChromeNetworkStack.Failure"/>