Remove blink::WebUserMediaClient

https://crrev.com/c/1756744 removed all usage of this class but didn't
remove the file.

Bug: 919392
Change-Id: Ifbf0aa85b1a93330105392ef514ed4503434a23f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1875104Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Henrique Ferreiro <hferreiro@igalia.com>
Cr-Commit-Position: refs/heads/master@{#708633}

third_party/blink/public/web/web_user_media_client.h

-/*
- * Copyright (C) 2011 Google Inc. All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions are
- * met:
- *
- *     * Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- *     * Redistributions in binary form must reproduce the above
- * copyright notice, this list of conditions and the following disclaimer
- * in the documentation and/or other materials provided with the
- * distribution.
- *     * Neither the name of Google Inc. nor the names of its
- * contributors may be used to endorse or promote products derived from
- * this software without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- */
-
-#ifndef THIRD_PARTY_BLINK_PUBLIC_WEB_WEB_USER_MEDIA_CLIENT_H_
-#define THIRD_PARTY_BLINK_PUBLIC_WEB_WEB_USER_MEDIA_CLIENT_H_
-
-#include <memory>
-
-#include "base/memory/scoped_refptr.h"
-#include "third_party/blink/public/platform/web_common.h"
-
-namespace blink {
-
-class WebApplyConstraintsRequest;
-class WebMediaStreamTrack;
-class WebUserMediaRequest;
-class WebUserMediaClient;
-
-class WebUserMediaClient {
- public:
-  virtual ~WebUserMediaClient() = default;
-
-  virtual void RequestUserMedia(const WebUserMediaRequest&) = 0;
-  virtual void CancelUserMediaRequest(const WebUserMediaRequest&) = 0;
-  virtual void ApplyConstraints(const WebApplyConstraintsRequest&) = 0;
-  virtual void StopTrack(const WebMediaStreamTrack&) = 0;
-  virtual void ContextDestroyed() = 0;
-};
-
-}  // namespace blink
-
-#endif  // THIRD_PARTY_BLINK_PUBLIC_WEB_WEB_USER_MEDIA_CLIENT_H_