Add //base dependency to rtc_base:rtc_event when building with chromium.
Add //base dependency to rtc_base:rtc_event when building with chromium.

Should fix flakes of the form:

In file included from ../../third_party/webrtc/rtc_base/platform_thread.cc:11:
In file included from ../../third_party/webrtc\rtc_base/platform_thread.h:17:
In file included from ../../third_party/webrtc_overrides\rtc_base/event.h:9:
In file included from ../..\base/synchronization/waitable_event.h:15:
In file included from ../..\base/win/scoped_handle.h:12:
../..\base/location.h(14,10):  fatal error: 'base/debug/debugging_buildflags.h' file not found
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Bug: chromium:799759
Change-Id: I24a329e944c3ec8324057d882f96648c10198022
Reviewed-on: https://webrtc-review.googlesource.com/64388
Reviewed-by: Oleh Prypin <5baa3e04f9bd6ba7a2a4b56625a3c84f19237cdb@webrtc.org>
Reviewed-by: Patrik Höglund <b486136ee68458b09c92c86c39f451c87d6ef6a1@webrtc.org>
Commit-Queue: Oleh Prypin <5baa3e04f9bd6ba7a2a4b56625a3c84f19237cdb@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#22608}
TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc