Add failed_once category to Sheriff-O-Matic.

Tools/GardeningServer/model/ct-failure-group.html

Index: Tools/GardeningServer/model/ct-failure-group.html
diff --git a/Tools/GardeningServer/model/ct-failure-group.html b/Tools/GardeningServer/model/ct-failure-group.html
index 812a2a5efaac998e5f0e7996e3e8759402c5198c..5406e70c8da2a854d238518d4f21c01dcd8ad869 100644
--- a/Tools/GardeningServer/model/ct-failure-group.html
+++ b/Tools/GardeningServer/model/ct-failure-group.html
@@ -47,8 +47,19 @@ CTFailureGroup.prototype._computeProperties = function() {
   if (this.isSnoozed) {
     this.category = 'snoozed';
   } else {
+    var totalFailures = 0;
+    this.failures.map(function(f) {

[ojan, 2014/09/05 18:39:44]

In the common case, this is going to do a ton of work that it doesn't need to.
As soon as the totalFailures is > 1, we can bail out of both loops. How about
writing this as helper function (e.g. _failedOnce) that does a nested for loop
and early returns a boolean?

This is on my mind because we recently had 7600 failures on tip of tree and
sheriff-o-matic basically became unusable due to excessive, unnecessary looping.
:(

+      var resultNodes = f.resultNodesByBuilder;
+      Object.keys(resultNodes, function(r) {
+        totalFailures += resultNodes[r].failingBuildCount;
+      }.bind(this));
+    });
+    if (totalFailures == 1) {
+      this.category = 'failed_once';

[ojan, 2014/09/05 18:39:44]

Nit: We don't have many cases of string values like this, so there's no standard
practice exactly, but I slightly lean towards camelcase (i.e. failedOnce).

+    } else {
+      this.category = 'default';
+    }
     // FIXME: crbug.com/400397 Split into: Whole step failure, Tree closer, Test failure, Flaky tests
-    this.category = 'default';
   }
 
   this.bug = this._annotation.bug;