Move UserActivityDetector to ui/base/user_activity/.

ui/base/BUILD.gn

Index: ui/base/BUILD.gn
diff --git a/ui/base/BUILD.gn b/ui/base/BUILD.gn
index a40aa8b3e9920f505c35dc2fb73de295e83e5345..6b034af05dbf4b99da72e6815079ea03baddd115 100644
--- a/ui/base/BUILD.gn
+++ b/ui/base/BUILD.gn
@@ -233,6 +233,9 @@ component("base") {
     "ui_base_switches_util.h",
     "ui_base_types.cc",
     "ui_base_types.h",
+    "user_activity/user_activity_detector.cc",
+    "user_activity/user_activity_detector.h",
+    "user_activity/user_activity_observer.h",
     "view_prop.cc",
     "view_prop.h",
     "webui/jstemplate_builder.cc",
@@ -741,8 +744,13 @@ test("ui_base_unittests") {
     "resource/resource_bundle_unittest.cc",
     "test/test_clipboard_unittest.cc",
     "test/run_all_unittests.cc",
+    "user_activity/user_activity_detector_unittest.cc",
   ]
 
+  if (is_android) {
+    sources -= [ "user_activity/user_activity_detector_unittest.cc" ]
+  }
+
   if (is_ios) {
     # Compile this Mac file on iOS as well.
     set_sources_assignment_filter([])