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

chrome/browser/webauth/authenticator_web_contents_manager.h

Index: chrome/browser/webauth/authenticator_web_contents_manager.h
diff --git a/chrome/browser/webauth/authenticator_web_contents_manager.h b/chrome/browser/webauth/authenticator_web_contents_manager.h
new file mode 100644
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+++ b/chrome/browser/webauth/authenticator_web_contents_manager.h
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+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_WEBAUTH_AUTHENTICATOR_WEB_CONTENTS_MANAGER_H_
+#define CHROME_BROWSER_WEBAUTH_AUTHENTICATOR_WEB_CONTENTS_MANAGER_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "components/webauth/authenticator.mojom.h"
+#include "content/public/browser/web_contents_user_data.h"
+#include "mojo/public/cpp/bindings/interface_request.h"
+
+// This class owns the Authenticator associated with a given WebContents.
+// The Authenticator is destroyed when the WebContents goes away.
+class AuthenticatorWebContentsManager
+    : public content::WebContentsUserData<AuthenticatorWebContentsManager> {
+ public:
+  ~AuthenticatorWebContentsManager() override;
+
+  // Retrieves the instance of AuthenticatorWebContentsManager that was
+  // attached to the specified WebContents.  If no instance was attached,
+  // creates one, and attaches it to the specified WebContents.
+  static AuthenticatorWebContentsManager* GetOrCreateForWebContents(
+      content::WebContents* web_contents);
+
+  // Creates the Authenticator that will interact with this |web_contents|.
+  void CreateAuthenticator(
+      content::RenderFrameHost* render_frame_host,
+      mojo::InterfaceRequest<webauth::mojom::Authenticator> authenticator);
+
+ private:
+  explicit AuthenticatorWebContentsManager(content::WebContents* web_contents);
+  friend class content::WebContentsUserData<AuthenticatorWebContentsManager>;
+
+  DISALLOW_COPY_AND_ASSIGN(AuthenticatorWebContentsManager);
+};
+
+#endif  // CHROME_BROWSER_WEBAUTH_AUTHENTICATOR_WEB_CONTENTS_MANAGER_H_