Only allow static strings as ProcessThread names.

Review URL: https://codereview.webrtc.org/1336293002

Cr-Commit-Position: refs/heads/master@{#9932}

webrtc/modules/utility/source/process_thread_impl.cc

@@ -77,7 +77,7 @@ void ProcessThreadImpl::Start() {
   }
 
   thread_ = ThreadWrapper::CreateThread(&ProcessThreadImpl::Run, this,
-                                        thread_name_.c_str());
+                                        thread_name_);
   CHECK(thread_->Start());
 }
 

webrtc/modules/utility/source/process_thread_impl.h

@@ -76,7 +76,7 @@ class ProcessThreadImpl : public ProcessThread {
   // TODO(tommi): Support delayed tasks.
   std::queue<ProcessTask*> queue_;
   bool stop_;
-  std::string thread_name_;
+  const char* thread_name_;
 };
 
 }  // namespace webrtc