Test RTC_DCHECK_IS_ON instead of checking DCHECK_ALWAYS_ON everywhere

The former is always defined (by webrtc/base/checks.h) to either 0 or
1, whereas the latter isn't necessarily defined.

This is a re-land of https://codereview.webrtc.org/2384693002, which
broke Chromium. We re-land without changing this CL at all, because
the thing that needed fixing was in Chromium:
https://codereview.chromium.org/2384263004.

NOTRY=true
TBR=ossu@webrtc.org
BUG=webrtc:6451

Review-Url: https://codereview.webrtc.org/2389943003
Cr-Commit-Position: refs/heads/master@{#14508}
diff --git a/webrtc/modules/utility/source/process_thread_impl.cc b/webrtc/modules/utility/source/process_thread_impl.cc
index 66534de..3332cd6 100644
--- a/webrtc/modules/utility/source/process_thread_impl.cc
+++ b/webrtc/modules/utility/source/process_thread_impl.cc
@@ -133,7 +133,7 @@
   RTC_DCHECK(thread_checker_.CalledOnValidThread());
   RTC_DCHECK(module);
 
-#if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON))
+#if RTC_DCHECK_IS_ON
   {
     // Catch programmer error.
     rtc::CritScope lock(&lock_);