TrustedTypes policy usage in viewLayer

[jrieken]

Continues #106285 (comment)

I have done the following measurement with the file attached below (uses the standalone editor). tt_N is run N using trusted types, str_N is run N with what we have today. I have picked _finishRenderingNewLines since that's where all changes are and insertAdjacentHTML which is receiving a trusted type

	_finishRenderingNewLines	insertAdjacentHTML
tt_1	20	17
tt_2	16	12
tt_3	17	13
str_1	17	16
str_2	15	13
str_3	16	15

sample.txt
profiles.zip

The first run with trusted types seems have been an outlier but otherwise I don't see a difference between both.

[jrieken]

Changes that I have done

diff --git a/src/vs/editor/browser/view/viewLayer.ts b/src/vs/editor/browser/view/viewLayer.ts
index eec48240c9..5ab9784cd4 100644
--- a/src/vs/editor/browser/view/viewLayer.ts
+++ b/src/vs/editor/browser/view/viewLayer.ts
@@ -369,6 +369,8 @@ interface IRendererContext<T extends IVisibleLine> {
 
 class ViewLayerRenderer<T extends IVisibleLine> {
 
+	private static _ttPolicy = window.trustedTypes?.createPolicy('editorViewLayer', { createHTML: value => value });
+
 	readonly domNode: HTMLElement;
 	readonly host: IVisibleLinesHost<T>;
 	readonly viewportData: ViewportData;
@@ -505,6 +507,9 @@ class ViewLayerRenderer<T extends IVisibleLine> {
 	}
 
 	private _finishRenderingNewLines(ctx: IRendererContext<T>, domNodeIsEmpty: boolean, newLinesHTML: string, wasNew: boolean[]): void {
+		if (ViewLayerRenderer._ttPolicy) {
+			newLinesHTML = ViewLayerRenderer._ttPolicy.createHTML(newLinesHTML) as unknown as string; // explains the ugly casts -> https://github.com/microsoft/vscode/issues/106396#issuecomment-692625393
+		}
 		const lastChild = <HTMLElement>this.domNode.lastChild;
 		if (domNodeIsEmpty || !lastChild) {
 			this.domNode.innerHTML = newLinesHTML;

[alexdima]

👍 Looks good, I tried with more heavy files.