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

chrome/test/BUILD.gn

Index: chrome/test/BUILD.gn
diff --git a/chrome/test/BUILD.gn b/chrome/test/BUILD.gn
index a2f3b3051d71897c4bdc8bdab58152cdd5c06357..cd0fce0be5d3c0fcec57e9d9b81ba03b46cdc2b3 100644
--- a/chrome/test/BUILD.gn
+++ b/chrome/test/BUILD.gn
@@ -3371,7 +3371,6 @@ test("unit_tests") {
     "../browser/ui/webui/local_state/local_state_ui_unittest.cc",
     "../browser/ui/webui/log_web_ui_url_unittest.cc",
     "../browser/update_client/chrome_update_query_params_delegate_unittest.cc",
-    "../browser/webshare/share_service_impl_unittest.cc",
     "../browser/webshare/share_target_pref_helper_unittest.cc",
     "../browser/win/chrome_elf_init_unittest.cc",
     "../browser/win/enumerate_modules_model_unittest.cc",
@@ -3791,6 +3790,10 @@ test("unit_tests") {
     ]
   }
 
+  if (is_linux || is_win) {
+    sources += [ "../browser/webshare/share_service_impl_unittest.cc" ]
+  }
+
   if (is_ios || is_chromeos) {
     sources -= [ "../browser/signin/chrome_signin_status_metrics_provider_delegate_unittest.cc" ]
   }