Refactor components_unittest build and deps

This CL,
-Removes BUILD.gn files from components/download/ and
  components/download/content/ directories
-changes components_unittests to depend on
 //components/download/internal:unit_tests and
 //components/download/content/internal:unit_tests directly.

Bug: None
Change-Id: I921594005bae407b1747f50a2a90b3c4cd722fe7
Reviewed-on: https://chromium-review.googlesource.com/554424
Commit-Queue: SUCHIT AGRAWAL <a.suchit@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#490738}

components/BUILD.gn

@@ -188,7 +188,6 @@ test("components_unittests") {
       "//components/discardable_memory/service:unit_tests",
       "//components/dom_distiller/content/browser:unit_tests",
       "//components/domain_reliability:unit_tests",
-      "//components/download/content:unit_tests",
       "//components/favicon/content:unit_tests",
       "//components/gcm_driver/instance_id:unit_tests",
       "//components/history/content/browser:unit_tests",

components/download/BUILD.gn

@@ -2,8 +2,6 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-# TODO(dtrainor): Remove this file and have components_unittests depend on
-# //components/download/internal:unit_tests directly.
 group("unit_tests") {
   testonly = true
 
@@ -11,6 +9,13 @@ group("unit_tests") {
     "//components/download/internal:unit_tests",
   ]
 
+  if (!is_ios) {
+    deps += [
+      "//components/download/content/internal:unit_tests",
+      "//components/download/content/public:unit_tests",
+    ]
+  }
+
   data_deps = [
     ":components_unittests_gtest_filter",
   ]

components/download/content/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.
-
-# TODO(dtrainor): Remove this file and have components_unittests depend on
-# //components/download/content/internal:unit_tests directly.
-group("unit_tests") {
-  testonly = true
-
-  deps = [
-    "//components/download/content/internal:unit_tests",
-    "//components/download/content/public:unit_tests",
-  ]
-}