Register metric Histogram names.

tracing/tracing/metrics/metric_map_function.html

Index: tracing/tracing/metrics/metric_map_function.html
diff --git a/tracing/tracing/metrics/metric_map_function.html b/tracing/tracing/metrics/metric_map_function.html
index a4f10972021338995dade1d19d7067bd850cbee3..1624436520901a545356c333e2e537bb5fbe5b27 100644
--- a/tracing/tracing/metrics/metric_map_function.html
+++ b/tracing/tracing/metrics/metric_map_function.html
@@ -21,27 +21,70 @@ tr.exportTo('tr.metrics', function() {
    * @return {!tr.v.HistogramSet}
    */
   function runMetrics(model, options) {
-    if (options === undefined)
+    if (options === undefined) {
       throw new Error('Options are required.');
+    }
 
     var metricNames = options.metrics;
-    if (!metricNames)
+    if (!metricNames) {
       throw new Error('Metric names should be specified.');
+    }
 
     var histograms = new tr.v.HistogramSet();
 
+    var metrics = [];
     for (var metricName of metricNames) {
       var metric = tr.metrics.MetricRegistry.findTypeInfoWithName(metricName);
-      if (metric === undefined)
+      if (metric === undefined) {
         throw new Error('"' + metricName + '" is not a registered metric.');
-      metric.constructor(histograms, model, options);
+      }
+      metrics.push(metric);
+      try {
+        metric.constructor(histograms, model, options);
+      } catch (e) {
+        synthesizeFailureHistograms(histograms, metric, e);
+      }
     }
 
+    validateHistogramNames(histograms, metrics);
+
     return histograms;
   }
 
   /**
    * @param {!tr.v.HistogramSet} histograms
+   * @param {!Array.<!tr.b.RegisteredTypeInfo>} metrics
+   */
+  function validateHistogramNames(histograms, metrics) {
+    var registeredHistogramNames = new Set();
+    for (var metric of metrics) {
+      for (var name of metric.metadata.histogramNames) {
+        registeredHistogramNames.add(name);
+      }
+    }
+    for (var hist of histograms) {
+      if (!registeredHistogramNames.has(hist.name)) {
+        throw new Error('"' + hist.name +
+                        '" is not a registered histogram name.');
+      }
+    }
+  }
+
+  /**
+   * @param {!tr.v.HistogramSet} histograms
+   * @param {!tr.b.RegisteredTypeInfo} metric
+   * @param {!Error} error
+   */
+  function synthesizeFailureHistograms(histograms, metric, error) {
+    for (var name of metric.metadata.histogramNames) {
+      var hist = new tr.v.Histogram(name, tr.b.Unit.byName.unitlessNumber);
+      // TODO(benjhayden): add a FailureInfo containing |error|.
+      histograms.addHistogram(hist);
+    }
+  }
+
+  /**
+   * @param {!tr.v.HistogramSet} histograms
    * @param {!tr.model.Model} model
    */
   function addTelemetryInfo(histograms, model) {