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..da3f8707eb2bb23ab1b088234b7c6c4dc9d657df 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.",

[Matt Perry, 2013/06/21 22:00:19]

nit: it's unclear to me whether "field trial exists" means that the field trial
is enabled in this client, or just that the field trial is a valid trial name.
could you clarify in the description?

[Oleg Eterevsky, 2013/06/22 19:53:08]

Added "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.",