Move common functionality of IOSChromeIOThread to ios/components.

ios/components/BUILD.gn

+# Copyright 2017 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.
+
+import("//ios/build/config.gni")
+import("//testing/test.gni")
+
+# All tests needs to be listed in that target to be built as part of
+# "gn_all" target (i.e. by the bots).
+group("all_tests") {
+  testonly = true
+  deps = [
+    ":ios_components_unittests",
+  ]
+}
+
+# To add a unit test to this target, make a "unit_tests" source_set in your
+# component (it's important to use a source_set instead of a static library or
+# no tests will run) and add a reference here. You can add more than one unit
+# test target if convenient.
+test("ios_components_unittests") {
+  # Add only ":unit_tests" dependencies here. If your tests have dependencies
+  # (this would at least include the component itself), they should be on the
+  # test source set and not here.
+
+  deps = [
+    "//base",
+    "//base/test:run_all_unittests",
+    "//ios/components/io_thread:unit_tests",
+  ]
+
+  assert_no_deps = ios_assert_no_deps
+}