[IndexedDB] Adding uma for transaction aborts

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 f454f6d977559f57c49c27f4dbb9421e964cdfb4..cc546f9193b5de008f35c9444f52debd85b68a95 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -80678,6 +80678,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="WebCore.IndexedDB.TransactionAbortReason" enum="IDBException">
+  <owner>dmurph@chromium.org</owner>
+  <summary>
+    Recorded on the browser side (back end) when an IndexedDB transaction is
+    aborted, specifically recording the reason for the abort. This can be
+    triggered by javascript code on the renderer, errors or force closes on the
+    backend, or by the transaction timeout timer.
+  </summary>
+</histogram>
+
 <histogram name="WebCore.PreloadDelayMs" units="ms">
   <owner>csharrison@chromium.org</owner>
   <summary>