Reason for revert:
Trying to fix the link error on the chromium FYI trybots.
Original issue's description:
> Revert of Decoupling rtc_base from Obj-C code (patchset #1 id:1 of https://codereview.webrtc.org/3004373002/ )
>
> Reason for revert:
> It breaks a chromium FYI trybot (the switch from rtc_static_library to rtc_source_set seems to be the problem).
>
> Original issue's description:
> > Reland of Decoupling rtc_base from Obj-C code (patchset #1 id:1 of https://codereview.webrtc.org/3008103002/ )
> >
> > Reason for revert:
> > Trying to reland after fixing downstream project.
> >
> > Original issue's description:
> > > Revert of Decoupling rtc_base from Obj-C code (patchset #8 id:140001 of https://codereview.webrtc.org/3001623003/ )
> > >
> > > Reason for revert:
> > > It breaks a downstream project.
> > >
> > > Original issue's description:
> > > > Decoupling rtc_base from Obj-C code
> > > >
> > > > The goal of this CL is to separate Obj-C/Obj-C++ code from targets which have
> > > > also C++ code (see https://bugs.chromium.org/p/webrtc/issues/detail?id=7743
> > > > for more information).
> > > >
> > > > To achieve this we have created 2 targets (rtc_base_objc and rtc_base_generic)
> > > > and rtc_base will act as a proxy between these targets (this way we can avoid a
> > > > circular dependency between rtc_base_generic and rtc_base_objc).
> > > >
> > > > BUG=webrtc:7743
> > > >
> > > > Review-Url: https://codereview.webrtc.org/3001623003
> > > > Cr-Commit-Position: refs/heads/master@{#19661}
> > > > Committed: a0a5b98937
> > >
> > > TBR=kjellander@webrtc.org,kwiberg@webrtc.org
> > > # Skipping CQ checks because original CL landed less than 1 days ago.
> > > NOPRESUBMIT=true
> > > NOTREECHECKS=true
> > > NOTRY=true
> > > BUG=webrtc:7743
> > >
> > > Review-Url: https://codereview.webrtc.org/3008103002
> > > Cr-Commit-Position: refs/heads/master@{#19664}
> > > Committed: 791a8f611d
> >
> > TBR=kjellander@webrtc.org,kwiberg@webrtc.org
> > # Skipping CQ checks because original CL landed less than 1 days ago.
> > NOPRESUBMIT=true
> > NOTREECHECKS=true
> > NOTRY=true
> > BUG=webrtc:7743
> >
> > Review-Url: https://codereview.webrtc.org/3004373002
> > Cr-Commit-Position: refs/heads/master@{#19681}
> > Committed: a0c893f324
>
> TBR=kjellander@webrtc.org,kwiberg@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=webrtc:7743
>
> Review-Url: https://codereview.webrtc.org/3007183002
> Cr-Commit-Position: refs/heads/master@{#19688}
> Committed: 9c5e511806TBR=kjellander@webrtc.org,kwiberg@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:7743
BUG=webrtc:7743
Review-Url: https://codereview.webrtc.org/3012823002
Cr-Commit-Position: refs/heads/master@{#19726}
310e32b92a