Disable WebAuthN for WebViews

WebAuthN is now enabled by default on Android but intentionally
is not supported by WebView

Bug: 875174
Change-Id: Iea94af1ed20884bcd6957ffb5057deb30cb8fb25
Reviewed-on: https://chromium-review.googlesource.com/1179964Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Kim Paulhamus <kpaulhamus@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584157}

android_webview/lib/aw_main_delegate.cc

@@ -162,6 +162,9 @@ bool AwMainDelegate::BasicStartupComplete(int* exit_code) {
 
   CommandLineHelper::AddDisabledFeature(*cl, features::kWebPayments.name);
 
+  // WebView does not and should not support WebAuthN.
+  CommandLineHelper::AddDisabledFeature(*cl, features::kWebAuth.name);
+
   // WebView isn't compatible with OOP-D.
   CommandLineHelper::AddDisabledFeature(*cl,
                                         features::kVizDisplayCompositor.name);