Suppress deprecation warnings in video_capture for iOS

The chromium_revision roll in r6913 broke the iOS build since the
videoMinFrameDuration and videoMaxFrameDuration properties
have been deprecated in iOS 7.0, which is now the default target
platform for iOS.

BUG=3705
TEST=Passing ios and ios_rel trybots.
TBR=tkchin@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/22389004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6914 4adac7df-926f-26a2-2b94-8c16560cd09d