Add a new webstorePrivate API to show a permission prompt for delegated installs
(i.e. remote installs for another user).

Also add a new permission prompt type for this case.

Design doc (slightly outdated wrt naming): https://docs.google.com/document/d/1gXvIt0TMMGVMWlIdaLZAGB_V2CbHO24-UL5WHL5siOc/edit#heading=h.bawdzzep787b

BUG=397951

Review URL: https://codereview.chromium.org/850283003

Cr-Commit-Position: refs/heads/master@{#318621}
diff --git a/extensions/browser/extension_function_histogram_value.h b/extensions/browser/extension_function_histogram_value.h
index 9f16451..319d2ac 100644
--- a/extensions/browser/extension_function_histogram_value.h
+++ b/extensions/browser/extension_function_histogram_value.h
@@ -1031,6 +1031,7 @@
   FILEMANAGERPRIVATE_SETENTRYTAG,
   INPUTMETHODPRIVATE_FETCHALLDICTIONARYWORDS,
   INPUTMETHODPRIVATE_ADDWORDTODICTIONARY,
+  WEBSTOREPRIVATE_SHOWPERMISSIONPROMPTFORDELEGATEDINSTALL,
   // Last entry: Add new entries above and ensure to update
   // tools/metrics/histograms/histograms.xml.
   ENUM_BOUNDARY