iOS: Add resource files for tests and implement OutputPath

With this change the following tests have been successfully
passing in the iOS Simulator for iPhone 5 and iOS 9:
* audio_decoder_unittests
* common_video_unittests
* modules_tests
* rtc_api_objc_tests
* rtc_pc_unittests
* system_wrappers_unittests
* voice_engine_unittests

The modules_unittests and common_audio_unittests are
handled in https://codereview.webrtc.org/1698033002/

BUG=webrtc:4755
NOTRY=True

Review URL: https://codereview.webrtc.org/1694353003

Cr-Commit-Position: refs/heads/master@{#11646}
diff --git a/webrtc/modules/video_coding/test/tester_main.cc b/webrtc/modules/video_coding/test/tester_main.cc
index 33ca820..1aa2780 100644
--- a/webrtc/modules/video_coding/test/tester_main.cc
+++ b/webrtc/modules/video_coding/test/tester_main.cc
@@ -21,7 +21,7 @@
 DEFINE_int32(height, 288, "Height in pixels of the frames in the input file.");
 DEFINE_int32(rtt, 0, "RTT (round-trip time), in milliseconds.");
 DEFINE_string(input_filename,
-              webrtc::test::ProjectRootPath() + "/resources/foreman_cif.yuv",
+              webrtc::test::ResourcePath("foreman_cif", "yuv"),
               "Input file.");
 DEFINE_string(output_filename,
               webrtc::test::OutputPath() +