Use spec-compliant algorithm for video content-capture deviceId selection in getUserMedia.

content/renderer/media/media_stream_constraints_util_video_content.cc

 // 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.
 
 #include "content/renderer/media/media_stream_constraints_util_video_content.h"
 
 #include <cmath>
 #include <utility>
 #include <vector>
 
@@ skipping 234 matching lines @@
   } else {
     DCHECK(candidates.device_id_set.IsEmpty());
     return VideoContentCaptureSourceSelectionResult(
         constraint_set.deviceId.name());
   }
 }
 
 }  // namespace
 
 VideoContentCaptureSourceSelectionResult::
+    VideoContentCaptureSourceSelectionResult()
+    : VideoContentCaptureSourceSelectionResult("") {}
+
+VideoContentCaptureSourceSelectionResult::
     VideoContentCaptureSourceSelectionResult(const char* failed_constraint_name)
     : failed_constraint_name_(failed_constraint_name) {}
 
 VideoContentCaptureSourceSelectionResult::
     VideoContentCaptureSourceSelectionResult(
         std::string device_id,
         const rtc::Optional<bool>& noise_reduction,
         media::VideoCaptureParams capture_params)
     : failed_constraint_name_(nullptr),
       device_id_(std::move(device_id)),
@@ skipping 57 matching lines @@
         candidates.Intersection(advanced_candidates);
     if (!intersection.IsEmpty())
       candidates = std::move(intersection);
   }
 
   DCHECK(!candidates.IsEmpty());
   return SelectResultFromCandidates(candidates, constraints.basic());
 }
 
 }  // namespace content