Clean up deprecated sources assignment filter in //third_party/blink/public

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

Bug: 1018739
Change-Id: Icafd03aab1c7ad98b8acdd7f96f64b34ba430c64
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2443129
Auto-Submit: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Mike West <mkwst@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813563}

third_party/blink/public/BUILD.gn

@@ -17,13 +17,6 @@ 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)
-
 group("blink") {
   public_deps = [ ":blink_headers" ]
   deps = [
@@ -128,9 +121,6 @@ source_set("blink_headers") {
     "platform/input/synchronous_input_handler_proxy.h",
     "platform/interface_registry.h",
     "platform/internet_disconnected_web_url_loader.h",
-    "platform/linux/web_sandbox_support.h",
-    "platform/mac/web_sandbox_support.h",
-    "platform/mac/web_scrollbar_theme.h",
     "platform/media/webmediaplayer_delegate.h",
     "platform/modules/mediastream/media_stream_types.h",
     "platform/modules/mediastream/secure_display_link_tracker.h",
@@ -404,13 +394,27 @@ source_set("blink_headers") {
     "web/web_widget.h",
     "web/web_widget_client.h",
     "web/web_window_features.h",
-    "web/win/web_font_rendering.h",
   ]
 
   if (is_debug || dcheck_always_on) {
     sources += [ "web/web_disallow_transition_scope.h" ]
   }
 
+  if (is_mac) {
+    sources += [
+      "platform/mac/web_sandbox_support.h",
+      "platform/mac/web_scrollbar_theme.h",
+    ]
+  }
+
+  if (is_linux || is_chromeos) {
+    sources += [ "platform/linux/web_sandbox_support.h" ]
+  }
+
+  if (is_win) {
+    sources += [ "web/win/web_font_rendering.h" ]
+  }
+
   public_configs = [
     ":blink_headers_config",