Allow local networking Info.plist insertion to fail (#78085)

packages/flutter_tools/bin/xcode_backend.sh

@@ -235,8 +235,10 @@ AddObservatoryBonjourService() {
   local built_products_plist="${BUILT_PRODUCTS_DIR}/${INFOPLIST_PATH}"
 
   if [[ ! -f "${built_products_plist}" ]]; then
-    EchoError "error: ${INFOPLIST_PATH} does not exist. The Flutter \"Thin Binary\" build phase must run after \"Copy Bundle Resources\"."
-    exit -1
+    # Very occasionally Xcode hasn't created an Info.plist when this runs.
+    # The file will be present on re-run.
+    echo "${INFOPLIST_PATH} does not exist. Skipping _dartobservatory._tcp NSBonjourServices insertion. Try re-building to enable \"flutter attach\"."
+    return
   fi
   # If there are already NSBonjourServices specified by the app (uncommon), insert the observatory service name to the existing list.
   if plutil -extract NSBonjourServices xml1 -o - "${built_products_plist}"; then

packages/flutter_tools/test/integration.shard/xcode_backend_test.dart

@@ -96,7 +96,7 @@ void main() {
       infoPlist = buildDirectory.childFile('Info.plist');
     });
 
-    test('fails when the Info.plist is missing', () async {
+    test('handles when the Info.plist is missing', () async {
       final ProcessResult result = await Process.run(
         xcodeBackendPath,
         <String>['test_observatory_bonjour_service'],
@@ -106,8 +106,8 @@ void main() {
           'INFOPLIST_PATH': 'Info.plist',
         },
       );
-      expect(result.stderr, startsWith('error: Info.plist does not exist.'));
-      expect(result.exitCode, isNot(0));
+      expect(result.stdout, contains('Info.plist does not exist.'));
+      expect(result.exitCode, 0);
     });
 
     const String emptyPlist = '''