mac: Add UMA metrics for Handoff.

BUG=380419

Review URL: https://codereview.chromium.org/686553003

Cr-Commit-Position: refs/heads/master@{#301735}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index d26c899..b118e850 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -248,6 +248,10 @@
       #"browser_app_shim"  TODO(GYP)
     ]
   }
+  if (is_mac || is_ios) {
+    sources += rebase_path(gypi_values.chrome_browser_mac_ios_sources,
+                           ".", "//chrome")
+  }
   if (cld2_data_source == "component") {
     sources += [
       "component_updater/cld_component_installer.cc",