Disable PerfTest.AppendResult on iOS.
Disable PerfTest.AppendResult on iOS.

It seems 'testing::internal::CaptureStdout()' causes problems
when running on real iOS devices.

No-Try: true
Bug: webrtc:8592
Change-Id: Ia7ee636034c6bd1a1ad7a4fb6a2d32e236f64205
Reviewed-on: https://webrtc-review.googlesource.com/27140
Reviewed-by: Patrik Höglund <b486136ee68458b09c92c86c39f451c87d6ef6a1@webrtc.org>
Commit-Queue: Edward Lemur <d05609f027dc667cc37492b1dc1bdea5d60fa82a@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#20948}
ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc