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

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

Index: third_party/WebKit/Source/devtools/front_end/source_frame/SourcesTextEditor.js
diff --git a/third_party/WebKit/Source/devtools/front_end/source_frame/SourcesTextEditor.js b/third_party/WebKit/Source/devtools/front_end/source_frame/SourcesTextEditor.js
index 7057ba607a69a4a19f8271e10539599101d469da..a70036a8182d48f7641da8933c1b38ed59741aa0 100644
--- a/third_party/WebKit/Source/devtools/front_end/source_frame/SourcesTextEditor.js
+++ b/third_party/WebKit/Source/devtools/front_end/source_frame/SourcesTextEditor.js
@@ -502,27 +502,16 @@ SourceFrame.SourcesTextEditor = class extends TextEditor.CodeMirrorTextEditor {
     delete this._muteTextChangedEvent;
   }
 
-  /**
-   * @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);
+    this.setMimeType(this.mimeType());
   }
 
   /**
+   * @override
    * @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');