Add mic indicator update event for speech2text

src/engine/runtime.js

@@ -457,6 +457,15 @@ class Runtime extends EventEmitter {
         return 'PERIPHERAL_SCAN_TIMEOUT';
     }
 
+    /**
+     * Event name for requesting an update of the indicator that shows that the
+     * microphone is being used to stream audio.
+     * @const {string}
+     */
+    static get UPDATE_MIC_INDICATOR () {
+        return 'UPDATE_MIC_INDICATOR';
+    }
+
     /**
      * Event name for reporting that blocksInfo was updated.
      * @const {string}
@@ -989,6 +998,10 @@ class Runtime extends EventEmitter {
         return isConnected;
     }
 
+    requestMicIndicatorUpdate (visible) {
+        this.emit(Runtime.UPDATE_MIC_INDICATOR, visible);
+    }
+
     /**
      * Retrieve the function associated with the given opcode.
      * @param {!string} opcode The opcode to look up.