Add RTC_FROM_HERE location information to two DCHECKs in ProcessThread.

webrtc/modules/utility/source/process_thread_impl.cc

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 100 matching lines @@
   {
     rtc::CritScope lock(&lock_);
     queue_.push(task.release());
   }
   wake_up_->Set();
 }
 
 void ProcessThreadImpl::RegisterModule(Module* module,
                                        const rtc::Location& from) {
   RTC_DCHECK(thread_checker_.CalledOnValidThread());
-  RTC_DCHECK(module);
+  RTC_DCHECK(module) << from.ToString();
 
 #if RTC_DCHECK_IS_ON
   {
     // Catch programmer error.
     rtc::CritScope lock(&lock_);
-    for (const ModuleCallback& mc : modules_)
-      RTC_DCHECK(mc.module != module);
+    for (const ModuleCallback& mc : modules_) {
+      RTC_DCHECK(mc.module != module)
+          << "Already registered here: " << mc.location.ToString() << "\n"
+          << "Now attempting from here: " << from.ToString();
+    }
   }
 #endif
 
   // Now that we know the module isn't in the list, we'll call out to notify
   // the module that it's attached to the worker thread.  We don't hold
   // the lock while we make this call.
   if (thread_.get())
     module->ProcessThreadAttached(this);
 
   {
@@ skipping 73 matching lines @@
     }
   }
 
   int64_t time_to_wait = next_checkpoint - rtc::TimeMillis();
   if (time_to_wait > 0)
     wake_up_->Wait(static_cast<unsigned long>(time_to_wait));
 
   return true;
 }
 }  // namespace webrtc