Reland of GN: Enable ARC for Mac and iOS in rtc_* templates (patchset #1 id:1 of https://codereview.webrtc.org/2827223003/ )

Reason for revert:
Relanding after fixing ARC issue.

Original issue's description:
> Revert of GN: Enable ARC for Mac and iOS in rtc_* templates (patchset #3 id:40001 of https://codereview.webrtc.org/2781713004/ )
>
> Reason for revert:
> Breaks mac build
>
> Original issue's description:
> > GN: Enable ARC for Mac and iOS in rtc_* templates
> >
> > Remove all uses of retain/release and NSAutoreleasePool.
> >
> > This makes transformation to Bazel easier.
> >
> > This CL subsumes https://codereview.webrtc.org/2778163002 and depends on https://codereview.webrtc.org/2784483002/
> >
> > BUG=webrtc:6412
> >
> > Review-Url: https://codereview.webrtc.org/2781713004
> > Cr-Commit-Position: refs/heads/master@{#17780}
> > Committed: https://chromium.googlesource.com/external/webrtc/+/6bda02b51dc00401d2a0d04be996ed10e5acac47
>
> TBR=kjellander@webrtc.org,magjed@webrtc.org,stefan@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=webrtc:6412
>
> Review-Url: https://codereview.webrtc.org/2827223003
> Cr-Commit-Position: refs/heads/master@{#17784}
> Committed: https://chromium.googlesource.com/external/webrtc/+/7c8786ae8f2d8481f74b0ab16eb91a8101fe51dc

TBR=kjellander@webrtc.org,magjed@webrtc.org,stefan@webrtc.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=webrtc:6412

Review-Url: https://codereview.webrtc.org/2834273002
Cr-Commit-Position: refs/heads/master@{#17836}
diff --git a/webrtc/sdk/objc/Framework/UnitTests/RTCPeerConnectionTest.mm b/webrtc/sdk/objc/Framework/UnitTests/RTCPeerConnectionTest.mm
index bd2db30..1797fea 100644
--- a/webrtc/sdk/objc/Framework/UnitTests/RTCPeerConnectionTest.mm
+++ b/webrtc/sdk/objc/Framework/UnitTests/RTCPeerConnectionTest.mm
@@ -53,11 +53,13 @@
   RTCMediaConstraints *contraints = [[RTCMediaConstraints alloc] initWithMandatoryConstraints:@{}
       optionalConstraints:nil];
   RTCPeerConnectionFactory *factory = [[RTCPeerConnectionFactory alloc] init];
-  RTCPeerConnection *peerConnection = [factory peerConnectionWithConfiguration:config
-      constraints:contraints delegate:nil];
 
-  RTCConfiguration *newConfig = peerConnection.configuration;
-
+  RTCConfiguration *newConfig;
+  @autoreleasepool {
+    RTCPeerConnection *peerConnection =
+        [factory peerConnectionWithConfiguration:config constraints:contraints delegate:nil];
+    newConfig = peerConnection.configuration;
+  }
   EXPECT_EQ([config.iceServers count], [newConfig.iceServers count]);
   RTCIceServer *newServer = newConfig.iceServers[0];
   RTCIceServer *origServer = config.iceServers[0];
diff --git a/webrtc/sdk/objc/Framework/UnitTests/avformatmappertests.mm b/webrtc/sdk/objc/Framework/UnitTests/avformatmappertests.mm
index 624eec3..cbc2e50 100644
--- a/webrtc/sdk/objc/Framework/UnitTests/avformatmappertests.mm
+++ b/webrtc/sdk/objc/Framework/UnitTests/avformatmappertests.mm
@@ -97,7 +97,6 @@
     CFRelease(_format);
     _format = nil;
   }
-  [super dealloc];
 }
 
 // Redefinition of AVCaptureDevice methods we want to mock.