avoid content override when updating local resource roots.

src/vs/workbench/contrib/notebook/browser/view/renderers/backLayerWebView.ts

@@ -24,6 +24,11 @@ import { IWorkbenchEnvironmentService } from 'vs/workbench/services/environment/
 import { dirname } from 'vs/base/common/resources';
 import { IWorkspaceContextService } from 'vs/platform/workspace/common/workspace';
 
+export interface WebviewIntialized {
+	__vscode_notebook_message: boolean;
+	type: 'initialized'
+}
+
 export interface IDimensionMessage {
 	__vscode_notebook_message: boolean;
 	type: 'dimension';
@@ -107,6 +112,7 @@ export interface IScrollRequestMessage {
 export interface IUpdatePreloadResourceMessage {
 	type: 'preload';
 	resources: string[];
+	source: string;
 }
 
 interface ICachedInset {
@@ -124,7 +130,7 @@ function html(strings: TemplateStringsArray, ...values: any[]): string {
 	return str;
 }
 
-type IMessage = IDimensionMessage | IScrollAckMessage | IWheelMessage | IMouseEnterMessage | IMouseLeaveMessage | IBlurOutputMessage;
+type IMessage = IDimensionMessage | IScrollAckMessage | IWheelMessage | IMouseEnterMessage | IMouseLeaveMessage | IBlurOutputMessage | WebviewIntialized;
 
 let version = 0;
 export class BackLayerWebView extends Disposable {
@@ -134,12 +140,12 @@ export class BackLayerWebView extends Disposable {
 	hiddenInsetMapping: Set<IOutput> = new Set();
 	reversedInsetMapping: Map<string, IOutput> = new Map();
 	preloadsCache: Map<string, boolean> = new Map();
-	kernelPreloadsCache: Map<string, boolean> = new Map();
 	localResourceRootsCache: URI[] | undefined = undefined;
 	rendererRootsCache: URI[] = [];
 	kernelRootsCache: URI[] = [];
 	private readonly _onMessage = this._register(new Emitter<any>());
 	public readonly onMessage: Event<any> = this._onMessage.event;
+	private _loaded!: Promise<void>;
 	private _initalized: Promise<void>;
 	private _disposed = false;
 
@@ -473,6 +479,11 @@ ${loaderJs}
 				}
 		}
 	});
+
+	vscode.postMessage({
+		__vscode_notebook_message: true,
+		type: 'initialized'
+	});
 }());
 
 </script>
@@ -584,6 +595,19 @@ ${loaderJs}
 			allowScripts: true,
 			localResourceRoots: this.localResourceRootsCache
 		}, undefined);
+
+		let resolveFunc: () => void;
+		this._loaded = new Promise<void>((resolve, reject) => {
+			resolveFunc = resolve;
+		});
+
+		let dispose = webview.onMessage((data: IMessage) => {
+			if (data.__vscode_notebook_message && data.type === 'initialized') {
+				resolveFunc();
+				dispose.dispose();
+			}
+		});
+
 		webview.html = content;
 		return webview;
 	}
@@ -744,11 +768,13 @@ ${loaderJs}
 		}, 50);
 	}
 
-	updateKernelPreloads(extensionLocations: URI[], preloads: URI[]) {
+	async updateKernelPreloads(extensionLocations: URI[], preloads: URI[]) {
 		if (this._disposed) {
 			return;
 		}
 
+		await this._loaded;
+
 		let resources: string[] = [];
 		preloads = preloads.map(preload => {
 			if (this.environmentService.isExtensionDevelopment && (preload.scheme === 'http' || preload.scheme === 'https')) {
@@ -758,9 +784,9 @@ ${loaderJs}
 		});
 
 		preloads.forEach(e => {
-			if (!this.kernelPreloadsCache.has(e.toString())) {
+			if (!this.preloadsCache.has(e.toString())) {
 				resources.push(e.toString());
-				this.kernelPreloadsCache.set(e.toString(), true);
+				this.preloadsCache.set(e.toString(), true);
 			}
 		});
 
@@ -769,14 +795,16 @@ ${loaderJs}
 		}
 
 		this.kernelRootsCache = [...extensionLocations, ...this.kernelRootsCache];
-		this._updatePreloads(resources);
+		this._updatePreloads(resources, 'kernel');
 	}
 
-	updateRendererPreloads(preloads: ReadonlySet<number>) {
+	async updateRendererPreloads(preloads: ReadonlySet<number>) {
 		if (this._disposed) {
 			return;
 		}
 
+		await this._loaded;
+
 		let resources: string[] = [];
 		let extensionLocations: URI[] = [];
 		preloads.forEach(preload => {
@@ -799,23 +827,23 @@ ${loaderJs}
 			}
 		});
 
+		if (!resources.length) {
+			return;
+		}
+
 		this.rendererRootsCache = extensionLocations;
-		this._updatePreloads(resources);
+		this._updatePreloads(resources, 'renderer');
 	}
 
-	private _updatePreloads(resources: string[]) {
+	private _updatePreloads(resources: string[], source: string) {
 		const mixedResourceRoots = [...(this.localResourceRootsCache || []), ...this.rendererRootsCache, ...this.kernelRootsCache];
 
-		this.webview.contentOptions = {
-			allowMultipleAPIAcquire: true,
-			allowScripts: true,
-			enableCommandUris: true,
-			localResourceRoots: mixedResourceRoots
-		};
+		this.webview.localResourcesRoot = mixedResourceRoots;
 
 		let message: IUpdatePreloadResourceMessage = {
 			type: 'preload',
-			resources: resources
+			resources: resources,
+			source: source
 		};
 
 		this.webview.sendMessage(message);

src/vs/workbench/contrib/webview/browser/baseWebviewElement.ts

@@ -6,6 +6,7 @@
 import { addClass } from 'vs/base/browser/dom';
 import { IMouseWheelEvent } from 'vs/base/browser/mouseEvent';
 import { Emitter } from 'vs/base/common/event';
+import { URI } from 'vs/base/common/uri';
 import { Disposable, IDisposable } from 'vs/base/common/lifecycle';
 import { IEnvironmentService } from 'vs/platform/environment/common/environment';
 import { ExtensionIdentifier } from 'vs/platform/extensions/common/extensions';
@@ -248,6 +249,10 @@ export abstract class BaseWebview<T extends HTMLElement> extends Disposable {
 		this.doUpdateContent();
 	}
 
+	public set localResourcesRoot(resources: URI[]) {
+		/** no op */
+	}
+
 	public set state(state: string | undefined) {
 		this.content = {
 			html: this.content.html,

src/vs/workbench/contrib/webview/browser/dynamicWebviewEditorOverlay.ts

@@ -7,6 +7,7 @@ import { Dimension } from 'vs/base/browser/dom';
 import { IMouseWheelEvent } from 'vs/base/browser/mouseEvent';
 import { memoize } from 'vs/base/common/decorators';
 import { Emitter, Event } from 'vs/base/common/event';
+import { URI } from 'vs/base/common/uri';
 import { Disposable, DisposableStore, MutableDisposable } from 'vs/base/common/lifecycle';
 import { IContextKey, IContextKeyService } from 'vs/platform/contextkey/common/contextkey';
 import { ExtensionIdentifier } from 'vs/platform/extensions/common/extensions';
@@ -174,6 +175,10 @@ export class DynamicWebviewEditorOverlay extends Disposable implements WebviewOv
 		this.withWebview(webview => webview.contentOptions = value);
 	}
 
+	public set localResourcesRoot(resources: URI[]) {
+		this.withWebview(webview => webview.localResourcesRoot = resources);
+	}
+
 	private readonly _onDidFocus = this._register(new Emitter<void>());
 	public readonly onDidFocus: Event<void> = this._onDidFocus.event;
 

src/vs/workbench/contrib/webview/browser/webview.ts

@@ -76,6 +76,7 @@ export interface WebviewExtensionDescription {
 export interface Webview extends IDisposable {
 	html: string;
 	contentOptions: WebviewContentOptions;
+	localResourcesRoot: URI[];
 	extension: WebviewExtensionDescription | undefined;
 	initialScrollProgress: number;
 	state: string | undefined;

src/vs/workbench/contrib/webview/electron-browser/webviewElement.ts

@@ -380,6 +380,11 @@ export class ElectronWebviewBasedWebview extends BaseWebview<WebviewTag> impleme
 		super.contentOptions = options;
 	}
 
+	public set localResourcesRoot(resources: URI[]) {
+		this._protocolProvider.update(resources || []);
+		super.localResourcesRoot = resources;
+	}
+
 	protected readonly extraContentOptions = {};
 
 	public set html(value: string) {