DevTools: [Sources] Improve editor load time by optimizing setMimeType

third_party/WebKit/Source/devtools/front_end/source_frame/SourcesTextEditor.js

 // Copyright (c) 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 /**
  * @unrestricted
  */
 SourceFrame.SourcesTextEditor = class extends TextEditor.CodeMirrorTextEditor {
   /**
    * @param {!SourceFrame.SourcesTextEditorDelegate} delegate
    */
@@ skipping 484 matching lines @@
    * @param {string} text
    */
   setText(text) {
     this._muteTextChangedEvent = true;
     this._setEditorIndentation(
         text.split('\n').slice(0, SourceFrame.SourcesTextEditor.LinesToScanForIndentationGuessing));
     super.setText(text);
     delete this._muteTextChangedEvent;
   }
 
+  _updateWhitespace() {
+    this.setMimeType(this.mimeType());
+  }
+
   /**
    * @override
    * @param {string} mimeType
-   * @return {!Promise}
-   */
-  setMimeType(mimeType) {
-    this._mimeType = mimeType;
-    return super.setMimeType(mimeType).then(
-        () => this._codeMirror.setOption('mode', this._applyWhitespaceMimetype(mimeType)));
-  }
-
-  _updateWhitespace() {
-    if (this._mimeType)
-      this.setMimeType(this._mimeType);
-  }
-
-  /**
-   * @param {string} mimeType
    * @return {string}
    */
-  _applyWhitespaceMimetype(mimeType) {
+  rewriteMimeType(mimeType) {
     this._setupWhitespaceHighlight();
     var whitespaceMode = Common.moduleSetting('showWhitespacesInEditor').get();
     this.element.classList.toggle('show-whitespaces', whitespaceMode === 'all');
 
     if (whitespaceMode === 'all')
       return this._allWhitespaceOverlayMode(mimeType);
     else if (whitespaceMode === 'trailing')
       return this._trailingWhitespaceOverlayMode(mimeType);
 
     return mimeType;
@@ skipping 377 matching lines @@
    */
   _setHighlighter(highlighter, selectionStart) {
     var overlayMode = {token: highlighter};
     this._codeMirror.addOverlay(overlayMode);
     this._highlightDescriptor = {overlay: overlayMode, selectionStart: selectionStart};
   }
 };
 
 SourceFrame.SourcesTextEditor.LinesToScanForIndentationGuessing = 1000;
 SourceFrame.SourcesTextEditor.MaximumNumberOfWhitespacesPerSingleSpan = 16;