Add a private API method metricsPrivate.getFieldTrial(), which returns

chrome/common/extensions/api/metrics_private.json

Index: chrome/common/extensions/api/metrics_private.json
diff --git a/chrome/common/extensions/api/metrics_private.json b/chrome/common/extensions/api/metrics_private.json
index 2e86f889b9ffdecab3568d7816e042cc2c943dbb..7b4f7b1be199ffa486793b064b8cf3ac5bf60303 100644
--- a/chrome/common/extensions/api/metrics_private.json
+++ b/chrome/common/extensions/api/metrics_private.json
@@ -41,6 +41,22 @@
         ]
       },
       {
+        "name": "getFieldTrial",
+        "description": "Returns the group name chosen for the named trial, or the empty string if the trial does not exist or is not enabled.",
+        "type": "function",
+        "parameters": [
+          {"name": "name", "type": "string"},
+          {
+            "name": "callback",
+            "type": "function",
+            "optional": "false",
+            "parameters": [
+              { "name": "group", "type": "string" }
+            ]
+          }
+        ]
+      },
+      {
         "name": "recordUserAction",
         "type": "function",
         "description": "Records an action performed by the user.",