Convert FieldTrialActivated to use mojo.

Manually tested by printf'ing the arguments to FieldTrialActivated. The
args looked the same as for ChromeRenderMessageFilter prior to this CL.

BUG=577685

Review-Url: https://codereview.chromium.org/2453313004
Cr-Commit-Position: refs/heads/master@{#437142}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 363b5eb0..47503147 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -387,6 +387,8 @@
     "favicon/large_icon_service_factory.h",
     "features.cc",
     "features.h",
+    "field_trial_recorder.cc",
+    "field_trial_recorder.h",
     "file_select_helper.cc",
     "file_select_helper.h",
     "file_select_helper_mac.mm",