Add initial components unit tests to GN build.

components/autocomplete/BUILD.gn

Index: components/autocomplete/BUILD.gn
diff --git a/components/autocomplete/BUILD.gn b/components/autocomplete/BUILD.gn
index 8341faf0baf566cae355522867a7a14c5c8f4e14..38e2a410917666bd9f6ab443b438ce6f7c680193 100644
--- a/components/autocomplete/BUILD.gn
+++ b/components/autocomplete/BUILD.gn
@@ -18,6 +18,10 @@ static_library("autocomplete") {
     "//net",
     "//url",
   ]
+
+  forward_dependent_configs_from = [
+    "//components/metrics/proto",
+  ]
 }
 
 static_library("test_support") {
@@ -32,3 +36,15 @@ static_library("test_support") {
     "//components/metrics/proto",
   ]
 }
+
+source_set("unit_tests") {
+  sources = [
+    "autocomplete_input_unittest.cc",
+  ]
+
+  deps = [
+    ":autocomplete",
+    ":test_support",
+    "//testing/gtest",
+  ]
+}