Make sure the default CSP is used for <webview> with PlzNavigate.

extensions/browser/extensions_browser_client.cc

Index: extensions/browser/extensions_browser_client.cc
diff --git a/extensions/browser/extensions_browser_client.cc b/extensions/browser/extensions_browser_client.cc
index 4e0f268fd542914f5d3bdf7eeedc725b96a860e0..8e7fe3e73a9b18964646d2eb00ff37b84e80bfc9 100644
--- a/extensions/browser/extensions_browser_client.cc
+++ b/extensions/browser/extensions_browser_client.cc
@@ -47,6 +47,12 @@ bool ExtensionsBrowserClient::IsActivityLoggingEnabled(
   return false;
 }
 
+ExtensionNavigationUIData*
+ExtensionsBrowserClient::GetExtensionNavigationUIData(
+    net::URLRequest* request) {
+  return nullptr;
+}
+
 ExtensionsBrowserClient* ExtensionsBrowserClient::Get() {
   return g_client;
 }