Fix the lit-html marker length to be consistently 9 characters. (#4570)

This was always how we intended it to behave, and since it didn't have a reliable length before this change this should be safe.

.changeset/young-roses-fly.md

@@ -0,0 +1,7 @@
+---
+'lit-html': patch
+'lit': patch
+'lit-element': patch
+---
+
+Fix the lit-html marker length to be consistently 9 characters.

packages/lit-html/src/lit-html.ts

@@ -336,7 +336,7 @@ const boundAttributeSuffix = '$lit$';
 // a valid element name and attribute name. We don't support dynamic names (yet)
 // but this at least ensures that the parse tree is closer to the template
 // intention.
-const marker = `lit$${String(Math.random()).slice(9)}$`;
+const marker = `lit$${Math.random().toFixed(9).slice(2)}$`;
 
 // String used to tell if a comment is a marker comment
 const markerMatch = '?' + marker;

scripts/check-size.js

@@ -9,8 +9,8 @@ import * as fs from 'fs';
 // it's likely that we'll ask you to investigate ways to reduce the size.
 //
 // In either case, update the size here and push a new commit to your PR.
-const expectedLitCoreSize = 15437;
-const expectedLitHtmlSize = 7252;
+const expectedLitCoreSize = 15443;
+const expectedLitHtmlSize = 7258;
 
 const litCoreSrc = fs.readFileSync('packages/lit/lit-core.min.js', 'utf8');
 const litCoreSize = fs.readFileSync('packages/lit/lit-core.min.js').byteLength;