Add Sparse Histogram Support to metricsPrivate

chrome/common/extensions/api/metrics_private.json

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 [
   {
     "namespace": "metricsPrivate",
     "description": "none",
     "types": [
       {
@@ skipping 130 matching lines @@
       {
         "name": "recordLongTime",
         "type": "function",
         "description": "Records an elapsed time of no more than 1 hour.  The sample value is specified in milliseconds.",
         "parameters": [
           {"name": "metricName", "type": "string"},
           {"name": "value", "type": "integer"}
         ]
       },
       {
+        "name": "recordSparseValue",
+        "type": "function",
+        "description": "Increments the count associated with |value| in the sparse histogram defined by the |metricName|",

[Ilya Sherman, 2014/03/26 22:44:14]

nit: Please end the sentence with a period.

[robliao, 2014/03/26 23:37:54]

Done.

+        "parameters": [
+          {"name": "metricName", "type": "string"},
+          {"name": "value", "type": "integer"}
+        ]
+      },
+      {
         "name": "recordValue",
         "type": "function",
         "description": "Adds a value to the given metric.",
         "parameters": [
           {"name": "metric", "$ref": "MetricType"},
           {"name": "value", "type": "integer"}
         ]
       }
     ],
     "events": []
   }
 ]