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

chrome/browser/BUILD.gn

Index: chrome/browser/BUILD.gn
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index fe9cc21de62a40c7cae9349d1ecda8c5729179c7..7e0a6021a4fde27f9b692c5ea633f70d0bc93589 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -1319,8 +1319,6 @@ split_static_library("browser") {
     "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",
@@ -3610,6 +3608,8 @@ split_static_library("browser") {
     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",
     ]
   }