Update our use of Sign In With Google to use FedCM. (#3668)

client-src/elements/chromedash-header.js

@@ -205,6 +205,7 @@ export class ChromedashHeader extends LitElement {
     google.accounts.id.initialize({
       client_id: this.googleSignInClientId,
       callback: this.handleCredentialResponse,
+      use_fedcm_for_prompt: true,
     });
     google.accounts.id.prompt();
 

framework/csp.py

@@ -31,6 +31,7 @@ NONCE_LENGTH = 30
 # Note: This is an addition beyond the reference csp.py example code.
 HOST_SOURCES = [
     'https://www.gstatic.com',
+    'https://accounts.google.com/gsi/client',
     ]
 
 DEFAULT_POLICY = {