Fix scheduleProofing method availability

See-also: 04c7f63b5cf62630e74da5949617831b515b6d03

service.js

@@ -186,6 +186,19 @@ class BesService {
     return this
   }
 
+  /**
+   * Schedules proofing after given number of milliseconds.
+   *
+   * @param {Number} timeout Number of milliseconds to delay proofing start
+   */
+  scheduleProofing(timeout) {
+    if (this.timer) clearTimeout(this.timer)
+    this.timer = setTimeout(() => {
+      this.proofAll()
+      delete this.timer
+    }, timeout)
+  }
+
   /**
    * Called initially when grammar-checking run is started
    */
@@ -521,19 +534,6 @@ class BesTreeService extends BesService {
     super.unregister()
   }
 
-  /**
-   * Schedules proofing after given number of milliseconds.
-   *
-   * @param {Number} timeout Number of milliseconds to delay proofing start
-   */
-  scheduleProofing(timeout) {
-    if (this.timer) clearTimeout(this.timer)
-    this.timer = setTimeout(() => {
-      this.proofAll()
-      delete this.timer
-    }, timeout)
-  }
-
   /**
    * Recursively grammar-(re)checks our host DOM tree.
    */