Replace the WAS_INSTALLED_BY_CUSTODIAN creation flag with a pref

extensions/browser/extension_prefs.h

Index: extensions/browser/extension_prefs.h
diff --git a/extensions/browser/extension_prefs.h b/extensions/browser/extension_prefs.h
index bae2126e755715670b87d5f5e1af6f103330df54..4bcd86b892e55bd402e87ecc479b26bc03361bd2 100644
--- a/extensions/browser/extension_prefs.h
+++ b/extensions/browser/extension_prefs.h
@@ -409,6 +409,14 @@ class ExtensionPrefs : public ExtensionScopedPrefs, public KeyedService {
   void SetAllowFileAccess(const std::string& extension_id, bool allow);
   bool HasAllowFileAccessSetting(const std::string& extension_id) const;
 
+  // Returns true if this extension has been installed by the custodian of
+  // a supervised user.  It is relevant for supervised users and used to block
+  // them from uninstalling the extension for example.
+  bool IsInstalledByCustodian(const std::string& extension_id) const;

[Marc Treib, 2016/06/13 09:37:14]

WasInstalledByCustodian please, to stay consistent with the install flag.

I'm not very happy with being both a pref and an install flag, but I guess
there's no way around it.

[mamir, 2016/06/13 11:30:17]

Done.
And I share the same feeling about being both a pref and a install flag.

[Marc Treib, 2016/06/13 12:17:09]

Hm. Do we still need the creation flag? (There's actually another thing called
"install flags" which is different...)
It seems that we could get rid of it and have all callers check the pref
instead, but I might be missing something.

[mamir, 2016/06/13 14:15:57]

Well, this was my 3rd proposal to tackle this issue (shared earlier in a doc).
I checked where the (installed_by_custodian) creation flag is used in the code,
and it looks like we can actually get rid of it.
But of course some corner case might be overlooked when switching from
creation_flags to a pref.
I will try that in another CL.

[Marc Treib, 2016/06/13 14:36:50]

Alright. If Devlin is okay with that, then I am too. :)

+  void SetIsInstalledByCustodian(const std::string& extension_id,
+                                 bool installed_by_custodian);
+  bool HasIsInstalledByCustodianSetting(const std::string& extension_id) const;
+
   // Saves ExtensionInfo for each installed extension with the path to the
   // version directory and the location. Blacklisted extensions won't be saved
   // and neither will external extensions the user has explicitly uninstalled.