Clean up deprecated sources assignment filter in //components/download

Remove deprecated_default_sources_assignment_filter and replace
it with explicit is_win, is_mac, etc. sections.

Bug: 1018739
Change-Id: I8244fafbe99305d3119d0c8243cc2a9236e9d3d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2445494Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813684}

components/download/internal/common/BUILD.gn

@@ -9,13 +9,6 @@ if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
-# This file depends on the legacy global sources assignment filter. It should
-# be converted to check target platform before assigning source files to the
-# sources variable. Remove this import and set_sources_assignment_filter call
-# when the file has been converted. See https://crbug.com/1018739 for details.
-import("//build/config/deprecated_default_sources_assignment_filter.gni")
-set_sources_assignment_filter(deprecated_default_sources_assignment_filter)
-
 source_set("internal") {
   visibility = [
     ":for_tests",
@@ -29,7 +22,6 @@ source_set("internal") {
   sources = [
     "all_download_event_notifier.cc",
     "base_file.cc",
-    "base_file_win.cc",
     "download_create_info.cc",
     "download_db_cache.cc",
     "download_db_cache.h",
@@ -109,6 +101,10 @@ source_set("internal") {
     deps += [ ":jni_headers" ]
   }
 
+  if (is_win) {
+    sources += [ "base_file_win.cc" ]
+  }
+
   if (is_posix || is_fuchsia) {
     sources += [ "base_file_posix.cc" ]
   }
@@ -156,7 +152,6 @@ source_set("unit_tests") {
   sources = [
     "all_download_event_notifier_unittest.cc",
     "base_file_unittest.cc",
-    "base_file_win_unittest.cc",
     "download_db_cache_unittest.cc",
     "download_file_unittest.cc",
     "download_item_impl_unittest.cc",
@@ -168,6 +163,10 @@ source_set("unit_tests") {
     "rate_estimator_unittest.cc",
   ]
 
+  if (is_win) {
+    sources += [ "base_file_win_unittest.cc" ]
+  }
+
   deps = [
     ":for_tests",
     "//base/test:test_support",