Introduce a stable set of errors for inline install

chrome/common/extensions/api/webstore/webstore_api_constants.h

Index: chrome/common/extensions/api/webstore/webstore_api_constants.h
diff --git a/chrome/common/extensions/api/webstore/webstore_api_constants.h b/chrome/common/extensions/api/webstore/webstore_api_constants.h
index 445a57b9b464863c799048ef0d1898da3d4111eb..f42327e993eb7925304babb3034fb0fb4fc8f9de 100644
--- a/chrome/common/extensions/api/webstore/webstore_api_constants.h
+++ b/chrome/common/extensions/api/webstore/webstore_api_constants.h
@@ -22,6 +22,12 @@ enum InstallStage {
   INSTALL_STAGE_INSTALLING,
 };
 
+// Result codes returned by WebstoreStandaloneInstaller and its subclasses.
+// IMPORTANT: Keep this list in sync with both the definition in
+// chrome/common/extensions/api/webstore.json and
+// chrome/common/extensions/webstore_install_result.h!
+extern const char* kInstallResultCodes[];
+
 extern const char kInstallStageDownloading[];
 extern const char kInstallStageInstalling[];
 extern const char kOnInstallStageChangedMethodName[];