Hotword Audio Verification App: Adds to hotwordPrivate API

Adds a function to hotwordPrivate API for the Hotword Audio Verification app with. This function allows the app to check which mode it should launch in.

BUG=390086

Review URL: https://codereview.chromium.org/528113003

Cr-Commit-Position: refs/heads/master@{#296641}
diff --git a/extensions/browser/extension_function_histogram_value.h b/extensions/browser/extension_function_histogram_value.h
index 161e6005..fab2dc18 100644
--- a/extensions/browser/extension_function_histogram_value.h
+++ b/extensions/browser/extension_function_histogram_value.h
@@ -955,6 +955,7 @@
   USB_GETCONFIGURATION,
   WEBVIEWINTERNAL_SETALLOWTRANSPARENCY,
   EASYUNLOCKPRIVATE_GETUSERINFO,
+  HOTWORDPRIVATE_GETLAUNCHSTATE,
   // Last entry: Add new entries above and ensure to update
   // tools/metrics/histograms/histograms.xml.
   ENUM_BOUNDARY