Only attempt to codesign service dylibs if a codesigning identity is provided. (#2735)

sky/build/sdk_xcode_harness/FlutterApplication.xcodeproj/project.pbxproj

@@ -214,7 +214,7 @@
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 			shellPath = /bin/sh;
-			shellScript = "SERVICE_FRAMEWORKS_DIR=${SOURCE_ROOT}/Frameworks\nSERVICE_DEFINITIONS=${SOURCE_ROOT}/ServiceDefinitions.json\nAPPLICATION_BUNDLE=${BUILT_PRODUCTS_DIR}/${WRAPPER_NAME}\n\n# Copy Service Dylibs\nif [ -d \"${SERVICE_FRAMEWORKS_DIR}\" ]; then\nditto ${SERVICE_FRAMEWORKS_DIR} ${APPLICATION_BUNDLE}/Frameworks\nfi\n\n# Copy Service Definitions\nif [ -f \"${SERVICE_DEFINITIONS}\" ]; then\ncp ${SERVICE_DEFINITIONS} ${APPLICATION_BUNDLE}/\nfi\n";
+			shellScript = "SERVICE_FRAMEWORKS_DIR=${SOURCE_ROOT}/Frameworks\nSERVICE_DEFINITIONS=${SOURCE_ROOT}/ServiceDefinitions.json\nAPPLICATION_BUNDLE=${BUILT_PRODUCTS_DIR}/${WRAPPER_NAME}\n\n# Copy Service Dylibs\nif [ -d \"${SERVICE_FRAMEWORKS_DIR}\" ]; then\nditto ${SERVICE_FRAMEWORKS_DIR} ${APPLICATION_BUNDLE}/Frameworks\nfi\n\nif [[ -n \"${EXPANDED_CODE_SIGN_IDENTITY}\" ]]; then\n\n# Codesign Service Dylibs if an identity is provided.\nDYLIBS=\"${APPLICATION_BUNDLE}/Frameworks/*.dylib\"\nfor dylib in $DYLIBS; do\nxcrun codesign                                      \\\n    --force                                         \\\n    --sign ${EXPANDED_CODE_SIGN_IDENTITY}           \\\n    --preserve-metadata=identifier,entitlements     \\\n    --timestamp=none                                \\\n    \"${dylib}\"                                      \\\n\ndone\n\nfi\n\n# Copy Service Definitions\nif [ -f \"${SERVICE_DEFINITIONS}\" ]; then\ncp ${SERVICE_DEFINITIONS} ${APPLICATION_BUNDLE}/\nfi\n";
 			showEnvVarsInLog = 0;
 		};
 /* End PBXShellScriptBuildPhase section */