Notify hotwording extension of microphone state change.

chrome/common/extensions/api/hotword_private.idl

Index: chrome/common/extensions/api/hotword_private.idl
diff --git a/chrome/common/extensions/api/hotword_private.idl b/chrome/common/extensions/api/hotword_private.idl
index 012ad647307d456a9db315ae04dfea833818f25b..a7ffeb1a2449eae7751a0094e8e50d36298dbca7 100644
--- a/chrome/common/extensions/api/hotword_private.idl
+++ b/chrome/common/extensions/api/hotword_private.idl
@@ -182,5 +182,8 @@ namespace hotwordPrivate {
     // Fired when the browser wants to find out whether the speaker model
     // exists.
     static void onSpeakerModelExists();
+
+    // Fired when the microphone state changes.
+    static void onMicrophoneStateChanged(boolean enabled);
   };
 };