Reland "iOS: Save perf results under Documents/perf_result.json"

This will require a manual roll to downstream projects, since
the //test:perf_test target was introduced.

This is a reland of 10a8e7a9b5261a7e3ce19900ba3511be3b5911f8
Original change's description:
> iOS: Save perf results under Documents/perf_result.json
>
> TBR=henrika@webrtc.org
>
> Bug: webrtc:7156
> Change-Id: Ib00992cce0007e0b5c9274340df1a892f810b0c5
> Reviewed-on: https://webrtc-review.googlesource.com/29202
> Commit-Queue: Edward Lemur <ehmaldonado@webrtc.org>
> Reviewed-by: Henrik Andreassson <henrika@webrtc.org>
> Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#21244}

R=henrika@webrtc.org, phoglund@webrtc.org

Bug: webrtc:7156
Change-Id: I85fc7bc5fce0894af90017b71b9952b61b523424
Reviewed-on: https://webrtc-review.googlesource.com/37643
Reviewed-by: Patrik Höglund <phoglund@google.com>
Reviewed-by: Henrik Andreassson <henrika@webrtc.org>
Commit-Queue: Edward Lemur <ehmaldonado@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21518}
diff --git a/modules/audio_coding/BUILD.gn b/modules/audio_coding/BUILD.gn
index 3a4bca1..1d6a70c8 100644
--- a/modules/audio_coding/BUILD.gn
+++ b/modules/audio_coding/BUILD.gn
@@ -1390,6 +1390,7 @@
       "../../rtc_base:rtc_base_approved",
       "../../system_wrappers",
       "../../system_wrappers:field_trial_api",
+      "../../test:perf_test",
       "../../test:test_support",
     ]
 
@@ -1895,6 +1896,7 @@
 
     deps = [
       ":isac_fix",
+      "../../test:perf_test",
       "../../test:test_support",
     ]