Do not build share_service_impl and associated test on Mac/Android.

chrome/browser/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//build/split_static_library.gni")
 import("//chrome/common/features.gni")
@@ skipping 1301 matching lines @@
     "usb/usb_chooser_context_factory.cc",
     "usb/usb_chooser_context_factory.h",
     "usb/usb_tab_helper.cc",
     "usb/usb_tab_helper.h",
     "usb/web_usb_histograms.cc",
     "usb/web_usb_histograms.h",
     "usb/web_usb_permission_provider.cc",
     "usb/web_usb_permission_provider.h",
     "web_data_service_factory.cc",
     "web_data_service_factory.h",
-    "webshare/share_service_impl.cc",
-    "webshare/share_service_impl.h",
     "webshare/share_target_pref_helper.cc",
     "webshare/share_target_pref_helper.h",
     "win/app_icon.cc",
     "win/app_icon.h",
     "win/browser_util.cc",
     "win/browser_util.h",
     "win/chrome_elf_init.cc",
     "win/chrome_elf_init.h",
     "win/chrome_select_file_dialog_factory.cc",
     "win/chrome_select_file_dialog_factory.h",
@@ skipping 2269 matching lines @@
       "payments/payment_request_factory.cc",
       "payments/payment_request_factory.h",
     ]
     deps += [ "//components/payments:payment_request_impl" ]
   }
 
   if (is_linux || is_win) {
     sources += [
       "renderer_context_menu/spelling_options_submenu_observer.cc",
       "renderer_context_menu/spelling_options_submenu_observer.h",
+      "webshare/share_service_impl.cc",
+      "webshare/share_service_impl.h",
     ]
   }
 
   if (is_desktop_linux) {
     # Desktop linux, doesn't count ChromeOS.
     sources += [
       "first_run/upgrade_util.cc",
       "first_run/upgrade_util_linux.cc",
       "first_run/upgrade_util_linux.h",
       "icon_loader_auralinux.cc",
@@ skipping 903 matching lines @@
       "media/pepper_cdm_test_constants.cc",
       "media/pepper_cdm_test_constants.h",
     ]
   }
 }
 
 service_manifest("preferences_manifest") {
   name = "preferences"
   source = "prefs/preferences_manifest.json"
 }