[Tango->FCM] Change the experiment name to match the trial config

Change-Id: If05f20ee2299704349e70ef13bd1ccec0463cd85
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1599450
Commit-Queue: Tatiana Gornak <melandory@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658560}

testing/variations/fieldtrial_testing_config.json

@@ -2024,7 +2024,7 @@
             ]
         }
     ],
-    "FCMInvalidationsExperiment": [
+    "FCMInvalidations": [
         {
             "platforms": [
                 "android",
@@ -2037,7 +2037,7 @@
             ],
             "experiments": [
                 {
-                    "name": "FCMInvalidationsEnabled",
+                    "name": "Enabled_FCMInvalidations_20190507",
                     "enable_features": [
                         "FCMInvalidations"
                     ]