feat(watcher): Debounce autoWatchBatchDelay

Closes karma-runner#2331

docs/config/01-configuration-file.md

@@ -89,8 +89,9 @@ These are all of the available configuration options.
 
 **Description:** When Karma is watching the files for changes, it tries to batch
 multiple changes into a single run so that the test runner doesn't try to start and restart running
-tests more than it should. The configuration setting tells Karma how long to wait (in milliseconds) after any changes
-have occurred before starting the test process again.
+tests more than it should, or restart while build files are not in a consistent state. The configuration setting
+tells Karma how long to wait (in milliseconds) from the last file change before starting
+the test process again, resetting the timer each time a file changes (i.e. [debouncing](https://davidwalsh.name/javascript-debounce-function)).
 
 
 ## basePath

lib/file-list.js

@@ -71,14 +71,14 @@ var List = function (patterns, excludes, emitter, preprocess, batchInterval) {
   var self = this
 
   // Emit the `file_list_modified` event.
-  // This function is throttled to the value of `batchInterval`
+  // This function is debounced to the value of `batchInterval`
   // to avoid spamming the listener.
   function emit () {
     self._emitter.emit('file_list_modified', self.files)
   }
-  var throttledEmit = _.throttle(emit, self._batchInterval, {leading: false})
+  var debouncedEmit = _.debounce(emit, self._batchInterval, {leading: false})
   self._emitModified = function (immediate) {
-    immediate ? emit() : throttledEmit()
+    immediate ? emit() : debouncedEmit()
   }
 }