Update build files to use webrtc_overrides in Chromium instead of overrides.

Update build files to use webrtc_overrides in Chromium instead of overrides.

This is a part of moving the overrides to Chromium. See bug comment #65 for all steps.

BUG=chromium:468375
Committed: https://crrev.com/baae0a8a6c873ddf812a5687b84638359b2e7e5b
Cr-Commit-Position: refs/heads/master@{#9996}

[Henrik Grunell WebRTC, 2015-09-18 14:26:47]

henrikg@webrtc.org changed reviewers:
+ kjellander@webrtc.org

[kjellander_webrtc, 2015-09-21 03:56:37]

lgtm

+ andresp (current sheriff): Please file bug+disable those flaky tests (see
trybot runs)

[Henrik Grunell WebRTC, 2015-09-21 08:45:40]

The CQ bit was checked by henrikg@webrtc.org

[Henrik Grunell WebRTC, 2015-09-21 08:45:41]

The patchset sent to the CQ was uploaded after l-g-t-m from
kjellander@webrtc.org
Link to the patchset: https://codereview.webrtc.org/1354933002/#ps20001 (title:
"Rebase.")

[commit-bot: I haz the power, 2015-09-21 08:45:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1354933002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1354933002/20001

[commit-bot: I haz the power, 2015-09-21 09:53:05]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-09-21 09:53:15]

Patchset 2 (id:??) landed as
https://crrev.com/baae0a8a6c873ddf812a5687b84638359b2e7e5b
Cr-Commit-Position: refs/heads/master@{#9996}

[Henrik Grunell WebRTC, 2015-09-21 10:29:18]

A revert of this CL (patchset #2 id:20001) has been created in
https://codereview.webrtc.org/1352423002/ by henrikg@webrtc.org.

The reason for reverting is: Breaks FYI bots.

ninja: error: '../../third_party/webrtc_overrides/webrtc/base/logging.cc',
needed by 'obj/third_party/webrtc_overrides/webrtc/base/rtc_base.logging.o',
missing and no known rule to make it
.