Add component for feature engagement tracking.

components/feature_engagement_tracker/BUILD.gn

Index: components/feature_engagement_tracker/BUILD.gn
diff --git a/components/feature_engagement_tracker/BUILD.gn b/components/feature_engagement_tracker/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..bf8ad79f8e74d5f7ac2ad291d13591ce3c01bfa7
--- /dev/null
+++ b/components/feature_engagement_tracker/BUILD.gn
@@ -0,0 +1,39 @@
+# Copyright 2017 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+if (is_android) {
+  import("//build/config/android/config.gni")
+  import("//build/config/android/rules.gni")
+}
+
+group("feature_engagement_tracker") {
+  visibility = [ "*" ]

[brettw, 2017/03/30 23:09:48]

You don't have to change it if you don't want, but this line isn't doing
anything (since public is the default).

[nyquist, 2017/03/30 23:12:47]

True. I'll keep it for now to remind myself. If I change it, I'll change it
across this whole component.

+
+  public_deps = [
+    "//components/feature_engagement_tracker/public",
+  ]
+
+  deps = [
+    "//components/feature_engagement_tracker/internal",
+  ]
+}
+
+group("unit_tests") {
+  testonly = true
+
+  deps = [
+    "//components/feature_engagement_tracker/internal:unit_tests",
+  ]
+}
+
+if (is_android) {
+  java_group("feature_engagement_tracker_java") {
+    visibility = [ "*" ]
+
+    deps = [
+      "//components/feature_engagement_tracker/internal:internal_java",
+      "//components/feature_engagement_tracker/public:public_java",
+    ]
+  }
+}