Add the Mojo implementation of authenticator.mojom's MakeCredential.

content/public/common/content_features.h

Index: content/public/common/content_features.h
diff --git a/content/public/common/content_features.h b/content/public/common/content_features.h
index 337220a778c0623b7d50b4c33e41d98afa638a15..238deb0c2a68708a249eddfd0ee9349cb173b9f0 100644
--- a/content/public/common/content_features.h
+++ b/content/public/common/content_features.h
@@ -63,6 +63,7 @@ CONTENT_EXPORT extern const base::Feature kTokenBinding;
 CONTENT_EXPORT extern const base::Feature kTouchpadAndWheelScrollLatching;
 CONTENT_EXPORT extern const base::Feature kVrShell;
 CONTENT_EXPORT extern const base::Feature kWebAssembly;
+CONTENT_EXPORT extern const base::Feature kWebAuth;

[jochen (gone - plz use gerrit), 2017/04/25 15:08:26]

Not sure whether this is too early for a feature? Typically, you only need that
to run a finch experiment for the launch. Until then, the
RuntimeEnabledFeatures.json5 already results in a command line arg being
generated for local testing.

[kpaulhamus, 2017/05/11 20:09:57]

In that case, would I still bind the interface in
chrome_content_browser_client.cc, just without it being behind a feature flag?
I'm not sure where else to do it where it can have access to the
renderframehost. (This is needed so the browser-side service can get the
origin).

 CONTENT_EXPORT extern const base::Feature kWebGLImageChromium;
 CONTENT_EXPORT extern const base::Feature kWebPayments;
 CONTENT_EXPORT extern const base::Feature kWebRtcEcdsaDefault;