Apps&Extensions for supervised users: Add Extension::WAS_INSTALLED_BY_CUSTODIAN flag and proto entry.

Currently, supervised users can not use Apps/Extensions at all. In the future, their custodian will be able to remotely install Apps/Extensions for them. This CL introduces a new extension flag and corresponding proto entry that marks these extensions, so we can allow only those in the client.

Relevant design doc section: https://docs.google.com/a/google.com/document/d/1rqahhrErR_HiZ04v-Skb_kvXeyOfnTvBPFvKwAxuf10/edit#heading=h.ptivtbjwlda5

BUG=390520

Review URL: https://codereview.chromium.org/353493002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@283522 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/browser/extensions/extension_sync_service.cc b/chrome/browser/extensions/extension_sync_service.cc
index e1b1af2..82d93bb 100644
--- a/chrome/browser/extensions/extension_sync_service.cc
+++ b/chrome/browser/extensions/extension_sync_service.cc
@@ -526,7 +526,8 @@
             extension_sync_data.update_url(),
             filter,
             kInstallSilently,
-            extension_sync_data.remote_install())) {
+            extension_sync_data.remote_install(),
+            extension_sync_data.installed_by_custodian())) {
       LOG(WARNING) << "Could not add pending extension for " << id;
       // This means that the extension is already pending installation, with a
       // non-INTERNAL location.  Add to pending_sync_data, even though it will