DevTools: Cache the original content on UISourceCode

third_party/WebKit/Source/devtools/front_end/snippets/ScriptSnippetModel.js

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 536 matching lines @@
  * @unrestricted
  */
 Snippets.SnippetsProject = class extends Bindings.ContentProviderBasedProject {
   /**
    * @param {!Workspace.Workspace} workspace
    * @param {!Snippets.ScriptSnippetModel} model
    */
   constructor(workspace, model) {
     super(workspace, 'snippets:', Workspace.projectTypes.Snippets, '', false /* isServiceProject */);
     this._model = model;
+    /** @type {!WeakMap<!Workspace.UISourceCode, !Promise<?string>>} */
+    this._originalContent = new WeakMap();
   }
 
   /**
    * @param {string} name
    * @param {!Common.ContentProvider} contentProvider
    * @return {!Workspace.UISourceCode}
    */
   addSnippet(name, contentProvider) {
     return this.addContentProvider(name, contentProvider);
   }
 
   /**
    * @override
    * @return {boolean}
    */
   canSetFileContent() {
     return true;
   }
+  /**
+   * @override
+   * @param {!Workspace.UISourceCode} uiSourceCode
+   * @return {!Promise<?string>}
+   */
+  requestOriginalFileContent(uiSourceCode) {
+    if (this._originalContent.has(uiSourceCode))
+      return this._originalContent.get(uiSourceCode);
+    var promise = super.requestOriginalFileContent(uiSourceCode);
+    this._originalContent.set(uiSourceCode, promise);
+    return promise;
+  }
 
   /**
    * @override
    * @param {!Workspace.UISourceCode} uiSourceCode
    * @param {string} newContent
-   * @param {function(?string)} callback
+   * @param {function()} callback
    */
   setFileContent(uiSourceCode, newContent, callback) {
-    this._model._setScriptSnippetContent(uiSourceCode.url(), newContent);
-    callback('');
+    this.requestOriginalFileContent(uiSourceCode).then(() => {
+      this._model._setScriptSnippetContent(uiSourceCode.url(), newContent);
+      callback();
+    });
   }
 
   /**
    * @override
    * @return {boolean}
    */
   canRename() {
     return true;
   }
 
@@ skipping 24 matching lines @@
    */
   deleteFile(url) {
     this._model.deleteScriptSnippet(url);
   }
 };
 
 /**
  * @type {!Snippets.ScriptSnippetModel}
  */
 Snippets.scriptSnippetModel = new Snippets.ScriptSnippetModel(Workspace.workspace);