Clean up deprecated sources assignment filter in //google_apis

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

Bug: 1018739
Change-Id: Ieec4e3400ce3fcfa77b184dbc509600a1e973bc7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2443093Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: David Roger <droger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813129}

google_apis/BUILD.gn

@@ -8,13 +8,6 @@ import("//extensions/buildflags/buildflags.gni")
 import("//testing/test.gni")
 import("//third_party/protobuf/proto_library.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)
-
 declare_args() {
   # You can set the variable 'use_official_google_api_keys' to true
   # to use the Google-internal file containing official API keys
@@ -161,13 +154,10 @@ template("google_apis_tmpl") {
     }
 
     if (is_apple) {
-      set_sources_assignment_filter([])
       sources += [
         "google_api_keys_mac.h",
         "google_api_keys_mac.mm",
       ]
-      set_sources_assignment_filter(
-          deprecated_default_sources_assignment_filter)
 
       frameworks = [ "Foundation.framework" ]
     }
@@ -261,9 +251,7 @@ test("google_apis_unittests") {
   }
 
   if (is_apple) {
-    set_sources_assignment_filter([])
     sources += [ "google_api_keys_mac_unittest.mm" ]
-    set_sources_assignment_filter(deprecated_default_sources_assignment_filter)
 
     deps += [ "//third_party/ocmock" ]
   }