Revert of Change g_webrtc_logging_delegate from process-level to RenderThread-level...

Revert of Change g_webrtc_logging_delegate from process-level to RenderThread-level (patchset #1 id:1 of https://codereview.chromium.org/889313003/)

Reason for revert:
This breaks webrtc logging.  It changes a global pointer to be a tls pointer, which doesn't work.

Original issue's description:
> Change g_webrtc_logging_delegate from process-level to RenderThread-level
>
> --single-process mode may happen crash in file of webrtc_logging.cc where code
> is CHECK(!g_webrtc_logging_delegate). The orginal code is to expect there to
> be only one g_webrtc_logging_delegate instance in a single render process.
> g_webrtc_logging_delegate is created when a RenderThreadImpl is created.
> But in --single-process model all RenderThreadImpl are created in browser
> process and so g_webrtc_logging_delegate may be created many times in a single
> process. Then CHECK(!g_webrtc_logging_delegate) will fail.
>
> In this patch will change g_webrtc_logging_delegate from process-level to
> RenderThread-Level. Since every render process will only keep one RenderThread.
>
> BUG=455573
>
> Committed: https://crrev.com/1fb332dc1f81bb05716342704b7f969af6921f3e
> Cr-Commit-Position: refs/heads/master@{#315131}

TBR=jinlong.zhai@samsung.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=455573

Review URL: https://codereview.chromium.org/931693002

Cr-Commit-Position: refs/heads/master@{#316506}