Make the API for TokenHighlightLayer slightly stricter

All usages pass in a container so this needn't be an optional argument
anymore.

Release-Notes: skip
Change-Id: I191d69b7801c7b886e1bc33eb35fbc871ca80b1e
diff --git a/polygerrit-ui/app/api/embed.ts b/polygerrit-ui/app/api/embed.ts
index 7ad5a4d..de2e1bf 100644
--- a/polygerrit-ui/app/api/embed.ts
+++ b/polygerrit-ui/app/api/embed.ts
@@ -23,7 +23,7 @@
       GrDiffCursor: {new (): GrDiffCursor};
       TokenHighlightLayer: {
         new (
-          container?: HTMLElement,
+          container: HTMLElement,
           listener?: TokenHighlightListener
         ): DiffLayer;
       };
diff --git a/polygerrit-ui/app/embed/diff/gr-diff-builder/token-highlight-layer.ts b/polygerrit-ui/app/embed/diff/gr-diff-builder/token-highlight-layer.ts
index d018517..b96b156 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-builder/token-highlight-layer.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-builder/token-highlight-layer.ts
@@ -101,7 +101,7 @@
   private updateTokenTask?: DelayedTask;
 
   constructor(
-    container: HTMLElement = document.documentElement,
+    container: HTMLElement,
     tokenHighlightListener?: TokenHighlightListener
   ) {
     this.tokenHighlightListener = tokenHighlightListener;