Metal rendering should account for cropping.

Also:
- added a rotation override to allow ignoring frame rotation
- fixed a couple of minor issues
- made it possible to run the MTKView without the DisplayLink

Bug: webrtc:9301
Change-Id: Ia83c152d9b6d45d56ceb80d287b5d3eacfaebddd
Reviewed-on: https://webrtc-review.googlesource.com/78282
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Anders Carlsson <andersc@webrtc.org>
Commit-Queue: Peter Hanspers <peterhanspers@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23452}

examples/objc/AppRTCMobile/ios/ARDVideoCallView.m

@@ -43,7 +43,9 @@ static CGFloat const kStatusBarHeight = 20;
   if (self = [super initWithFrame:frame]) {
 
 #if defined(RTC_SUPPORTS_METAL)
-    _remoteVideoView = [[RTCMTLVideoView alloc] initWithFrame:CGRectZero];
+    RTCMTLVideoView *metalView = [[RTCMTLVideoView alloc] initWithFrame:CGRectZero];
+    metalView.useDisplayLink = NO;
+    _remoteVideoView = metalView;
 #else
     RTCEAGLVideoView *remoteView = [[RTCEAGLVideoView alloc] initWithFrame:CGRectZero];
     remoteView.delegate = self;