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

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

Bug: 1018739
Change-Id: If5db7645ff89b7071b2e7360c1f43496ba331d57
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2445478Reviewed-by: Wei Li <weili@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813692}

components/printing/renderer/BUILD.gn

@@ -2,18 +2,10 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-# 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)
-
 static_library("renderer") {
   sources = [
     "print_render_frame_helper.cc",
     "print_render_frame_helper.h",
-    "print_render_frame_helper_mac.mm",
   ]
 
   deps = [
@@ -30,4 +22,8 @@ static_library("renderer") {
     "//third_party/blink/public/common",
     "//ui/base",
   ]
+
+  if (is_mac) {
+    sources += [ "print_render_frame_helper_mac.mm" ]
+  }
 }