Add rtc_event_log_unittest_helper.h to relevant BUILD.gn
Add rtc_event_log_unittest_helper.h to relevant BUILD.gn

BUG=None

Review-Url: https://codereview.webrtc.org/3002813002
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#19389}

TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc