Adds components/history tests to BUILD.gn

components/history/content/browser/BUILD.gn

 # Copyright 2015 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.
 
 static_library("browser") {
   sources = [
     "content_visit_delegate.cc",
     "content_visit_delegate.h",
     "download_constants_utils.cc",
     "download_constants_utils.h",
     "history_context_helper.cc",
     "history_context_helper.h",
     "history_database_helper.cc",
     "history_database_helper.h",
     "web_contents_top_sites_observer.cc",
     "web_contents_top_sites_observer.h",
   ]
 
   deps = [
     "//base",
     "//components/history/core/browser",
     "//components/visitedlink/browser",
     "//content/public/browser",
     "//url:url",
   ]
 }
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "content_history_backend_db_unittest.cc",
+  ]
+  deps = [
+    ":browser",
+    "//components/history/core/browser:browser",
+    "//components/history/core/test",
+    "//testing/gtest",
+  ]
+}