Re-implement the screensaver to use WebView instead of ExtensionDialogHost.

ash/shell/shell_delegate_impl.cc

Index: ash/shell/shell_delegate_impl.cc
diff --git a/ash/shell/shell_delegate_impl.cc b/ash/shell/shell_delegate_impl.cc
index 9cafd1e682b0486ad09b37b9ee30195ff1cf9930..31edb6abc4a716519827d89a66a2eec9ff093631 100644
--- a/ash/shell/shell_delegate_impl.cc
+++ b/ash/shell/shell_delegate_impl.cc
@@ -75,6 +75,10 @@ void ShellDelegateImpl::OpenCrosh() {
 void ShellDelegateImpl::OpenMobileSetup() {
 }
 
+content::BrowserContext* ShellDelegateImpl::GetCurrentBrowserContext() {
+  return Shell::GetInstance()->browser_context();
+}
+
 void ShellDelegateImpl::ToggleSpokenFeedback() {
 }