Add field trial config for the DataSaverSiteBreakdownUsingPageLoadMetrics feature

Bug: 836029
Change-Id: Ia0f2a3608eb9be51b652b2519365737276e4f2c6
Reviewed-on: https://chromium-review.googlesource.com/1175558Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: rajendrant <rajendrant@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583402}

testing/variations/fieldtrial_testing_config.json

@@ -1251,6 +1251,25 @@
             ]
         }
     ],
+    "DataSaverSiteBreakdownUsingPageLoadMetrics": [
+        {
+            "platforms": [
+                "android",
+                "windows",
+                "mac",
+                "chromeos",
+                "linux"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "DataSaverSiteBreakdownUsingPageLoadMetrics"
+                    ]
+                }
+            ]
+        }
+    ],
     "DecoupleTranslateLanguage": [
         {
             "platforms": [