Basic UkmService implementation

ios/chrome/browser/metrics/BUILD.gn

Index: ios/chrome/browser/metrics/BUILD.gn
diff --git a/ios/chrome/browser/metrics/BUILD.gn b/ios/chrome/browser/metrics/BUILD.gn
index 9e4e7182c998487e679f3d09f3dfbb9ba5ce068d..05509b293088b2dc06b066af117a74df44906621 100644
--- a/ios/chrome/browser/metrics/BUILD.gn
+++ b/ios/chrome/browser/metrics/BUILD.gn
@@ -26,6 +26,7 @@ source_set("metrics") {
   deps = [
     "//base",
     "//components/crash/core/common",
+    "//components/keyed_service/core",
     "//components/keyed_service/ios",
     "//components/metrics",
     "//components/metrics:net",
@@ -39,6 +40,8 @@ source_set("metrics") {
     "//components/signin/core/browser",
     "//components/sync",
     "//components/translate/core/browser",
+    "//components/ukm",
+    "//components/ukm:observers",
     "//components/variations",
     "//components/variations/service",
     "//components/version_info",
@@ -46,6 +49,7 @@ source_set("metrics") {
     "//ios/chrome/browser/browser_state",
     "//ios/chrome/browser/crash_report",
     "//ios/chrome/browser/google",
+    "//ios/chrome/browser/history:history",
     "//ios/chrome/browser/signin",
     "//ios/chrome/browser/sync",
     "//ios/chrome/browser/tabs",