DevTools: Cache the original content on UISourceCode

third_party/WebKit/Source/devtools/front_end/persistence/FileSystemWorkspaceBinding.js

Index: third_party/WebKit/Source/devtools/front_end/persistence/FileSystemWorkspaceBinding.js
diff --git a/third_party/WebKit/Source/devtools/front_end/persistence/FileSystemWorkspaceBinding.js b/third_party/WebKit/Source/devtools/front_end/persistence/FileSystemWorkspaceBinding.js
index 8091642bebe380935fc48ef7a856273015a9bb6b..607200b689b33c966bbf3b9fb283ccd1d06c3e2e 100644
--- a/third_party/WebKit/Source/devtools/front_end/persistence/FileSystemWorkspaceBinding.js
+++ b/third_party/WebKit/Source/devtools/front_end/persistence/FileSystemWorkspaceBinding.js
@@ -196,6 +196,9 @@ Persistence.FileSystemWorkspaceBinding.FileSystem = class extends Workspace.Proj
 
     super(workspace, id, Workspace.projectTypes.FileSystem, displayName);
 
+    /** @type {!WeakMap<!Workspace.UISourceCode, !Promise<?string>>} */
+    this._originalContent = new WeakMap();
+
     this._fileSystem = isolatedFileSystem;
     this._fileSystemBaseURL = this._fileSystem.path() + '/';
     this._fileSystemWorkspaceBinding = fileSystemWorkspaceBinding;
@@ -286,6 +289,21 @@ Persistence.FileSystemWorkspaceBinding.FileSystem = class extends Workspace.Proj
 
   /**
    * @override
+   * @param {!Workspace.UISourceCode} uiSourceCode
+   * @return {!Promise<?string>}
+   */
+  requestOriginalFileContent(uiSourceCode) {
+    if (this._originalContent.has(uiSourceCode))
+      return this._originalContent.get(uiSourceCode);
+    var fulfill;
+    var promise = new Promise(x => fulfill = x);
+    this.requestFileContent(uiSourceCode, fulfill);
+    this._originalContent.set(uiSourceCode, promise);
+    return promise;
+  }
+
+  /**
+   * @override
    * @return {boolean}
    */
   canSetFileContent() {
@@ -296,11 +314,12 @@ Persistence.FileSystemWorkspaceBinding.FileSystem = class extends Workspace.Proj
    * @override
    * @param {!Workspace.UISourceCode} uiSourceCode
    * @param {string} newContent
-   * @param {function(?string)} callback

[einbinder, 2016/12/20 03:10:34]

The parameter in the callback was never used.

+   * @param {function()} callback
    */
   setFileContent(uiSourceCode, newContent, callback) {
     var filePath = this._filePathForUISourceCode(uiSourceCode);
-    this._fileSystem.setFileContent(filePath, newContent, callback.bind(this, ''));

[einbinder, 2016/12/20 03:10:34]

Bind the callback to this?! What is going on.

+    this.requestOriginalFileContent(uiSourceCode)
+        .then(() => this._fileSystem.setFileContent(filePath, newContent, callback));
   }
 
   /**