[Chromecast] Treat chrome-extension scheme as 'secure' in cast_shell

Currently the chrome-extension scheme is treated as 'insecure' in
cast_shell, and that makes service worker unavailable in cast_shell.
Add chrome-extension scheme to secure_schemes to solve this.

Bug: internal b/111359399
Test: check window.isSecureContext is true
Change-Id: Ic1d68ceac3b522f2c0140910d53e664fd9ff895d
Reviewed-on: https://chromium-review.googlesource.com/c/1308914
Commit-Queue: Jiawei Li <lijiawei@chromium.org>
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604349}

chromecast/common/cast_content_client.cc

@@ -90,6 +90,10 @@ void CastContentClient::AddAdditionalSchemes(Schemes* schemes) {
   schemes->standard_schemes.push_back(kChromeResourceScheme);
 #if BUILDFLAG(ENABLE_CHROMECAST_EXTENSIONS)
   schemes->standard_schemes.push_back(extensions::kExtensionScheme);
+  // Treat as secure because we only load extension code written by us.
+  schemes->secure_schemes.push_back(extensions::kExtensionScheme);
+  schemes->service_worker_schemes.push_back(extensions::kExtensionScheme);
+  schemes->csp_bypassing_schemes.push_back(extensions::kExtensionScheme);
 #endif
 }