Convert media constants to constexpr.

media/capture/video/mac/video_capture_device_avfoundation_mac.mm

 // Copyright 2013 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.
 
 #import "media/capture/video/mac/video_capture_device_avfoundation_mac.h"
 
 #import <CoreMedia/CoreMedia.h>
 #import <CoreVideo/CoreVideo.h>
 #include <stddef.h>
 #include <stdint.h>
@@ skipping 463 matching lines @@
 
   {
     base::AutoLock lock(lock_);
     const CoreMediaGlue::CMTime cm_timestamp =
         CoreMediaGlue::CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
     const base::TimeDelta timestamp =
         CMTIME_IS_VALID(cm_timestamp)
             ? base::TimeDelta::FromMicroseconds(
                   cm_timestamp.value * base::TimeTicks::kMicrosecondsPerSecond /
                   cm_timestamp.timescale)
-            : media::kNoTimestamp();
+            : media::kNoTimestamp;
 
     if (frameReceiver_ && baseAddress) {
       frameReceiver_->ReceiveFrame(reinterpret_cast<uint8_t*>(baseAddress),
                                    frameSize, captureFormat, 0, 0, timestamp);
     }
   }
 
   if (videoFrame)
     CVPixelBufferUnlockBaseAddress(videoFrame, kCVPixelBufferLock_ReadOnly);
 }
 
 - (void)onVideoError:(NSNotification*)errorNotification {
   NSError* error = base::mac::ObjCCast<NSError>([[errorNotification userInfo]
       objectForKey:AVFoundationGlue::AVCaptureSessionErrorKey()]);
   [self sendErrorString:[NSString
                             stringWithFormat:@"%@: %@",
                                              [error localizedDescription],
                                              [error localizedFailureReason]]];
 }
 
 - (void)sendErrorString:(NSString*)error {
   DLOG(ERROR) << [error UTF8String];
   base::AutoLock lock(lock_);
   if (frameReceiver_)
     frameReceiver_->ReceiveError(FROM_HERE, [error UTF8String]);
 }
 
 @end