Don't register or use the DelegateExecute verb handler if it isn't present.

chrome/installer/util/browser_distribution.h

Index: chrome/installer/util/browser_distribution.h
diff --git a/chrome/installer/util/browser_distribution.h b/chrome/installer/util/browser_distribution.h
index e62e03034a7d9b7d59d8090a3997eef3afd54cbc..db4020d1ed55f36d488a704afdfcd72f771480db 100644
--- a/chrome/installer/util/browser_distribution.h
+++ b/chrome/installer/util/browser_distribution.h
@@ -122,6 +122,9 @@ class BrowserDistribution {
   // |type_lib_uuid| and |type_lib_version| identify its type library.
   // |interface_uuid| is the ICommandExecuteImpl interface UUID.
   // Only non-null parameters will be set, others will be ignored.
+  // Implementations that only provide a DelegateExecute handler for use on
+  // certain OS versions must only return true when run on those supported
+  // systems.
   virtual bool GetDelegateExecuteHandlerData(string16* handler_class_uuid,
                                              string16* type_lib_uuid,
                                              string16* type_lib_version,