When building the WebRTC project for iOS, the build will fail on Xcode 9
because of a missing framework-header (AVFoundation). This pull-request
will add the missing "#import <AVFoundation/AVFoundation.h>" line to the
"RTCCameraVideoCapturer" class.
BUG=webrtc:7846
Review-Url: https://codereview.webrtc.org/2944753002
Cr-Commit-Position: refs/heads/master@{#18698}