Bug 1276714 - Add about:crashes telemetry r=BenWa,bsmedberg

MozReview-Commit-ID: 11GfIgkC5q6

toolkit/components/telemetry/Histograms.json

@@ -10874,5 +10874,13 @@
     "kind": "count",
     "releaseChannelCollection": "opt-out",
     "description": "Counts the number of times that about:tabcrashed was unloaded without submitting."
+  },
+  "ABOUTCRASHES_OPENED_COUNT": {
+    "alert_emails": ["bgirard@mozilla.com"],
+    "expires_in_version": "55",
+    "kind": "count",
+    "bug_numbers": [1276714, 1276716],
+    "description": "Number of times about:crashes has been opened.",
+    "releaseChannelCollection": "opt-out"
   }
 }

toolkit/crashreporter/content/crashes.js

@@ -50,6 +50,9 @@ function submitPendingReport(event) {
 }
 
 function populateReportList() {
+
+  Services.telemetry.getHistogramById("ABOUTCRASHES_OPENED_COUNT").add(1);
+
   var prefService = Cc["@mozilla.org/preferences-service;1"].
                     getService(Ci.nsIPrefBranch);