Add a name to the ProcessThread constructor.

Helps differentiate between different instances when debugging.

Review URL: https://codereview.webrtc.org/1337003003

Cr-Commit-Position: refs/heads/master@{#9927}
diff --git a/webrtc/modules/utility/source/process_thread_impl.h b/webrtc/modules/utility/source/process_thread_impl.h
index 1fd2bf3..53b5d59 100644
--- a/webrtc/modules/utility/source/process_thread_impl.h
+++ b/webrtc/modules/utility/source/process_thread_impl.h
@@ -25,7 +25,7 @@
 
 class ProcessThreadImpl : public ProcessThread {
  public:
-  ProcessThreadImpl();
+  explicit ProcessThreadImpl(const char* thread_name);
   ~ProcessThreadImpl() override;
 
   void Start() override;
@@ -76,6 +76,7 @@
   // TODO(tommi): Support delayed tasks.
   std::queue<ProcessTask*> queue_;
   bool stop_;
+  std::string thread_name_;
 };
 
 }  // namespace webrtc