Add a metrics extensions API....

chrome/common/extensions/api/extension_api.json

 [
   {
     "namespace": "extension",
     "unprivileged": true,
     "types": [
       {
         "id": "MessageSender",
         "type": "object",
         "description": "An object containing information about the script context that sent a message or request.",
         "properties": {
@@ skipping 2238 matching lines @@
                 "description": "Details about the tab's process."
               }
             ]
           }
         ]
       }
     ],
     "events": []
   },
   {
+    "namespace": "metrics",
+    "types": [
+      {
+        "id": "MetricType",
+        "type":  "object",
+        "description": "Describes the type of metric that is to be collected.",
+        "properties": {
+          "metricName": {"type": "string", "description": "A unique name within the extension for the metric."},
+          "type": {
+            "type": "string",
+            "enum": ["histogram-log", "histogram-linear"],
+            "description": "The type of metric, such as 'histogram-log' or 'histogram-linear'."
+          },
+          "min": {"type": "integer", "description": "The minimum sample value to be recoded.  Must be greater than zero."},
+          "max": {"type": "integer", "description": "The maximum sample value to be recoded."},
+          "buckets": {"type": "integer", "description": "The number of buckets to use when separating the recorded values."}
+        }
+      }
+    ],
+    "functions": [
+      {
+        "name": "recordUserAction",
+        "type": "function",
+        "description": "Records an action performed by the user.",
+        "parameters": [
+          {"name": "name", "type": "string"}
+        ]
+      },
+      {
+        "name": "recordPercentage",
+        "type": "function",
+        "description": "Record a percentage value from 1 to 100.",
+        "parameters": [
+          {"name": "metricName", "type": "string"},
+          {"name": "value", "type": "integer"}
+        ]
+      },
+      {
+        "name": "recordCount",
+        "type": "function",
+        "description": "Record a value than can range from 1 to 1,000,000.",
+        "parameters": [
+          {"name": "metricName", "type": "string"},
+          {"name": "value", "type": "integer"}
+        ]
+      },
+      {
+        "name": "recordSmallCount",
+        "type": "function",
+        "description": "Record a value than can range from 1 to 100.",
+        "parameters": [
+          {"name": "metricName", "type": "string"},
+          {"name": "value", "type": "integer"}
+        ]
+      },
+      {
+        "name": "recordMediumCount",
+        "type": "function",
+        "description": "Record a value than can range from 1 to 10,000.",
+        "parameters": [
+          {"name": "metricName", "type": "string"},
+          {"name": "value", "type": "integer"}
+        ]
+      },
+      {
+        "name": "recordTime",
+        "type": "function",
+        "description": "Record an elapsed time of no more than 10 seconds.  The sample value is specified in milliseconds.",
+        "parameters": [
+          {"name": "metricName", "type": "string"},
+          {"name": "value", "type": "integer"}
+        ]
+      },
+      {
+        "name": "recordMediumTime",
+        "type": "function",
+        "description": "Record an elapsed time of no more than 3 minutes.  The sample value is specified in milliseconds.",
+        "parameters": [
+          {"name": "metricName", "type": "string"},
+          {"name": "value", "type": "integer"}
+        ]
+      },
+      {
+        "name": "recordLongTime",
+        "type": "function",
+        "description": "Record 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": "recordValue",
+        "type": "function",
+        "unprivileged": true,
+        "description": "Adds a value to the given metric.",
+        "parameters": [
+          {"name": "metric", "$ref": "MetricType"},
+          {"name": "value", "type": "integer"}
+        ]
+      }
+    ],
+    "events": []
+  },
+  {
     "namespace": "test",
     "nodoc": true,
     "types": [],
     "functions": [
       {
         "name": "notifyFail",
         "type": "function",
         "description": "Notify the browser process that test code running in the extension failed.  This is only used for internal unit testing.",
         "parameters": [
           {"type": "string", "name": "message"}
@@ skipping 26 matching lines @@
         "type": "function",
         "description": "Creates an incognito tab during internal testing. Succeeds even if the extension is not enabled in incognito mode.",
         "parameters": [
           {"type": "string", "name": "url"}
         ]
       }
     ],
     "events": []
   }
 ]