Revert of Replace the remaining scoped_ptr with unique_ptr in webrtc/modules/ (patchset #1 id:40001 of https://codereview.webrtc.org/1921233002/ )

Reason for revert:
Fails on Chromium FYI bots.

https://build.chromium.org/p/chromium.webrtc.fyi/builders/Linux%20Builder/builds/5392/

Original issue's description:
> Replace the remaining scoped_ptr with unique_ptr in webrtc/modules/
>
> BUG=webrtc:5520
>
> Committed: https://crrev.com/2c27a062ee46258abe9facc2cceee74f09bf6a99
> Cr-Commit-Position: refs/heads/master@{#12511}

TBR=tommi@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:5520

Review URL: https://codereview.webrtc.org/1924443002

Cr-Commit-Position: refs/heads/master@{#12513}
diff --git a/webrtc/modules/utility/source/process_thread_impl.cc b/webrtc/modules/utility/source/process_thread_impl.cc
index 68c7ab6..8cdf016 100644
--- a/webrtc/modules/utility/source/process_thread_impl.cc
+++ b/webrtc/modules/utility/source/process_thread_impl.cc
@@ -36,9 +36,9 @@
 ProcessThread::~ProcessThread() {}
 
 // static
-std::unique_ptr<ProcessThread> ProcessThread::Create(
+rtc::scoped_ptr<ProcessThread> ProcessThread::Create(
     const char* thread_name) {
-  return std::unique_ptr<ProcessThread>(new ProcessThreadImpl(thread_name));
+  return rtc::scoped_ptr<ProcessThread>(new ProcessThreadImpl(thread_name));
 }
 
 ProcessThreadImpl::ProcessThreadImpl(const char* thread_name)
@@ -119,7 +119,7 @@
   wake_up_->Set();
 }
 
-void ProcessThreadImpl::PostTask(std::unique_ptr<ProcessTask> task) {
+void ProcessThreadImpl::PostTask(rtc::scoped_ptr<ProcessTask> task) {
   // Allowed to be called on any thread.
   {
     rtc::CritScope lock(&lock_);