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 6c414b50992f681586c41b86d57124acdde001d2..78cddbc0d82c64f2658646ebbb68a1573b0b10c8 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -1321,8 +1321,6 @@ 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",
@@ -3604,6 +3602,8 @@ split_static_library("browser") {
       "payments/payment_request_factory.h",
       "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",
     ]
     deps += [ "//components/payments:payment_request_impl" ]
   }