iOS SDK 10.0 compatability.

This CL adds support targeting iOS 10 as a min version.

Bug: None
Change-Id: I353a9884eb907e97387553fd73427fd7cb0dbfc2
Reviewed-on: https://webrtc-review.googlesource.com/79921
Reviewed-by: Anders Carlsson <andersc@webrtc.org>
Commit-Queue: Kári Helgason <kthelgason@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23461}

sdk/objc/Framework/Classes/UI/RTCEAGLVideoView.m

@@ -45,8 +45,11 @@
         [CADisplayLink displayLinkWithTarget:self
                                     selector:@selector(displayLinkDidFire:)];
     _displayLink.paused = YES;
-    // Set to half of screen refresh, which should be 30fps.
+#if __IPHONE_OS_VERSION_MIN_REQUIRED >= __IPHONE_10_0
+    _displayLink.preferredFramesPerSecond = 30;
+#else
     [_displayLink setFrameInterval:2];
+#endif
     [_displayLink addToRunLoop:[NSRunLoop currentRunLoop]
                        forMode:NSRunLoopCommonModes];
   }