Do not try to make Chrome default when registering it if it can't be made default unattended.

chrome/installer/setup/install.h

Index: chrome/installer/setup/install.h
diff --git a/chrome/installer/setup/install.h b/chrome/installer/setup/install.h
index 4ce974b5c0026f4d4578f59f72144dfa956d59d1..70ae28582ebbd179b613ccef87938808225ab598 100644
--- a/chrome/installer/setup/install.h
+++ b/chrome/installer/setup/install.h
@@ -80,10 +80,11 @@ void CreateOrUpdateShortcuts(
     InstallShortcutOperation install_operation);
 
 // Registers Chrome on this machine.
-// If |make_chrome_default|, also attempts to make Chrome default (potentially
-// popping a UAC if the user is not an admin and HKLM registrations are required
-// to register Chrome's capabilities on this version of Windows (i.e.
-// pre-Win8)).
+// If |make_chrome_default|, also attempts to make Chrome default.

[grt (UTC plus 2), 2013/03/05 03:27:10]

is this shorter form correct?
// If |make_chrome_default|, also attempts to make Chrome default where doing so
// requires no more user interaction than a UAC prompt. In practice, this means
// on versions of Windows prior to Windows 8.

[gab, 2013/03/05 16:29:32]

Much better :)!

+// |make_chrome_default| is ignored if Chrome can't be made default unattended
+// (except if the only user action required is to accept a UAC; e.g., if the
+// user is not an admin and HKLM registrations are required to register Chrome's
+// capabilities on this version of Windows (i.e. pre-Win8)).
 void RegisterChromeOnMachine(const InstallerState& installer_state,
                              const Product& product,
                              bool make_chrome_default);