Filed as radar 33760222 (https://openradar.appspot.com/33760222)

When building something that uses AVFoundation, such as media/capture/video/mac/video_capture_device_avfoundation_mac.mm, with Xcode 9 beta 5 (9M202q), clang produces errors like:

In file included from media/capture/video/mac/video_capture_device_avfoundation_mac.mm:5:
/Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/System/Library/Frameworks/AVFoundation.framework/Headers/AVFoundation.h:88:9: fatal error: 
      'AVFoundation/AVRouteDetector.h' file not found
#import <AVFoundation/AVRouteDetector.h>
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

The 10.13 SDK in Xcode 9b5 doesn’t include <AVFoundation/AVRouteDetector.h>, although <AVFoundation/AVFoundation.h> #imports this file. (This new file was present in the SDKs included in 9b2, 9b3, and 9b4).