Merge from vscode 79a1f5a5ca0c6c53db617aa1fa5a2396d2caebe2

src/vs/workbench/api/browser/mainThreadWebview.ts

@@ -325,13 +325,14 @@ export class MainThreadWebviews extends Disposable implements extHostProtocol.Ma
 			throw new Error(`Provider for ${viewType} already registered`);
 		}
 
-		this._customEditorService.registerCustomEditorCapabilities(viewType, {
-			supportsMultipleEditorsPerDocument
-		});
-
 		const extension = reviveWebviewExtension(extensionData);
 
 		const disposables = new DisposableStore();
+
+		disposables.add(this._customEditorService.registerCustomEditorCapabilities(viewType, {
+			supportsMultipleEditorsPerDocument
+		}));
+
 		disposables.add(this._webviewWorkbenchService.registerResolver({
 			canResolve: (webviewInput) => {
 				return webviewInput instanceof CustomEditorInput && webviewInput.viewType === viewType;
@@ -360,6 +361,17 @@ export class MainThreadWebviews extends Disposable implements extHostProtocol.Ma
 				}
 
 				webviewInput.webview.onDispose(() => {
+					// If the model is still dirty, make sure we have time to save it
+					if (modelRef.object.isDirty()) {
+						const sub = modelRef.object.onDidChangeDirty(() => {
+							if (!modelRef.object.isDirty()) {
+								sub.dispose();
+								modelRef.dispose();
+							}
+						});
+						return;
+					}
+
 					modelRef.dispose();
 				});
 
@@ -649,10 +661,11 @@ class MainThreadCustomEditorModel extends Disposable implements ICustomEditorMod
 	) {
 		super();
 
+		this._fromBackup = fromBackup;
+
 		if (_editable) {
 			this._register(workingCopyService.registerWorkingCopy(this));
 		}
-		this._fromBackup = fromBackup;
 	}
 
 	get editorResource() {
@@ -710,7 +723,7 @@ class MainThreadCustomEditorModel extends Disposable implements ICustomEditorMod
 	//#endregion
 
 	public isReadonly() {
-		return this._editable;
+		return !this._editable;
 	}
 
 	public get viewType() {